Other than English and Spanish, what would be a very useful language to learn?

Morse code

I've gained a lot in my life learning Urdu and Hindi and encourage more people to learn. They are essentially the same language with different scripts, but unlike Arabic or Chinese they are Indo European languages and are much easier to learn. I grew up speaking farsi so maybe it was easier for me but if you work in IT knowing Hindi is indispensable.

I'm gonna second French and Arabic for sheer amount of speakers (native or as secondary language), as well as geographic variety.

Other than that, I would've said that Russian would serve you well in the post-soviet sphere of influence, but that changed recently for obvious reasons. You very likely don't want to travel to Russia, and her neighbors don't look to kindly on Russian either, now. Will still do in a pinch

okay, and one joke answer: Japanese, you'll find weebs to talk to in every country

It depends on your goals, and what cultures are you interested in.

I'm also fluent in Spanish and English (native Spanish though), and my third language of choice has always been between Chinese or Japanese. I like east asian culture, technology and many of their cultural exports. So it was an easy choice for me (easy the choice, languages... not so easy).

If you don't know where you're going: French is probably the most wide spread after that.

I just (I mean an hour ago) gave up on learning japanese via Duo Lingo. On and off for years but didn't make considerable progress. I know about 20 hiragana symbols and a bit of vocabulary but I think I won't ever grasp order of words or how they communicate without plurals or genders. It's so different from germanic languages. I love the japanese culture but I just don't have the time anymore.

I instead started spanish. After a few lessons Duo Lingo rated me as a super learner. Don't know if it's because they want to sell me a subscription but I really flew through the lessons (even when I had to type out the sentences). I'll stay with it and will add dutch soon.

Python

Early adopter of that one. ~1994 IIRC

Kinda surprised that no one has mentioned sign language. I feel that it's use cases expand outside the original intent, especially if other people in your circle understand it.

But OP was asking about travelling the world. Sign language wouldn't help with that.

Sign language isn't one language. There's American Sign Language, British Sign Language, Australian Sign Language, Nigerian Sign Language, etc.

American Sign Language and British Sign Language are completely unintelligible to each other.
- That's a good point. I guess I just read the title and everyone else's comments saying stuff like "Python" and "TypeScript"
How many different standards are there for sign?
- Basically every country has their own sign language or an imported sign language that became standardized.
  
  But learning any sign language will make it a lot easier for you to communicate with signers of any sign language. Not because they’re necessarily similar to each other, but because sign language varies a lot regionally anyway (and even locally depending on what method of signing you’re taught) and it will be much more natural to find ways to work around it and communicate with each other.

French and Arabic are the second and third most spoken language in number of countries. Then there is the obvious Mandarin which is spoken in most of China with around a billion locutors

I keep debating Mandarin but my issue is how the language is tied tightly to China. Helpful if I decide to explore China in depth but seemingly less so if I want to "get by" in a large number of countries. If I had an ability to learn languages quickly, I would probably learn French, Mandarin, Arabic, and Hindi, but I think I am already pushing my limits.
- Yeah, that's the thing: "which language is spoken by the most people" is an easy question to answer, but "which language (or combination of languages) lets me communicate well enough to get by in the most places" is much harder because the statistics aren't necessarily collected in a way that lend themselves to that kind of analysis.
  
  For example, Hindi is spoken by a whole bunch of people, but I'm pretty sure the vast majority of those people also speak English, so if you already know English you don't actually need to learn it.

Depends on the route you want to take while traveling. For example, if you want to circumnavigate in a sailboat through the tropics, French is a great choice because France includes a bunch of tropical islands:

French is also widely spoken in Africa, IIRC.

There are more French speakers in Africa than there are in France and the French Language Authority is absolutley SEETHING at this fact because they're losing control over "proper French" and for the first time ever French is evolving like a language should
- There are also french speakers in Canada.
I wonder if most of those countries people don't speak either English or Spanish as a second language. As opposed to certain specific languages and countries were most people don't have or use much a second language like for example in Japan or Brazil
- In most of the places French is spoken, it is the second language (instead of English or Spanish). Only place I can think of off the top of my head where Francophones would likely also know English is Quebec and, I guess, France itself.
  
  The other languages in the sorts of places I was talking about are mostly ones like Arabic, various sub-Saharan African indigenous languages, or Polynesian.

Typescript

Since you're interested in traveling, I would say french. It is spoken in a very wide variety of countries all over the world, you have a lot of resources to learn it and it's related to the other languages to know. Other languages might have more speakers, but if youre just interested in the visiting a lot of wholly different places, it is probably the best one.

Lots of French loan words are also used by other languages.

I'd say French or Portuguese

By the numbers: French or Arabic, as other commenters have mentioned.

But it really, really depends on where in the world you want to travel. If you're interested in Asia, for example, neither French nor Spanish nor Arabic will help you much (save for some remaining French usage in Vietnam).

A better answer is: figure out where you want to go, then do the math on what to learn.

If you're fluent in Spanish you can probably bullshit your way through comprehending most romantic languages so French and Portuguese (the other big colonial languages) are probably out.

Maybe Arabic for the fact that while it isn't a dominant language in most countries there are fluent communities in all sorts of parts of the world.

Alternatively, Hindi/Mandarin for the sheer number of people it'd let you communicate with.

Fluency in spanish doesn't help with french in my experience. While both might be romance languages, french pronounciation makes it so that in conversation words are really, really hard to translate without prior knowledge on some words, at least for me. My first language is spanish, for reference. Portuguese and italian are a 50/50 depending on the accent.
Plus fluent in Spanish opens up travel to pretty much all of South America, Mexico, and Spain. There are differences in dialect, and some South American countries speak Portuguese, but you'll still be able to communicate.

Mandarain opens up communication with over a billion people

You say “travel the world,” but where realistically will you travel? Westerners tend to travel almost exclusively to other imperial core countries and to popular tourist spots in the periphery that cater to imperial core tourists.

Realistically, not India/Pakistan. Other than that I will likely hit the Americas, Europe, Oceania, Thailand, Vietnam, Shanghai, Singapore, maybe South Korea, Japan, UAE, Morrocco for sure, Turkey, etc. So, quite a bit I hope.
- Arabic and Chinese then.
what would be your recommendation for an american reddit leftist like me who has started plans on traveling to satisfy a desire to travel outside the american empire?

i can't figure out how to do it in a way that doesn't imperil me because of the those same vulnerability minority identities that the dnc failed to leverage as a cover for the genocide and virtue signal to shut out dissent from among their ranks and costed the whole country in this election.

i have an idea of what life is like for the people at the periphery of the core in north america and i want to know how much worse it is fully outside the core. it now makes sense that why the people want to hold imperialist friendly mexican judges accountable via the ballot box in a system that's completely captured by the american empire to social engineer the masses like it does when it makes a voter in tempe, arizona wait in line for hours to go vote.
- I don’t fully understand your question, and I doubt that I’m qualified to answer, because I have virtually every privilege, and I’ve never thought about international travel but from my own easy mode perspective.

The Harappan language—then you could decipher the script of the Indus Valley civilization.

D rink yo ur ov alt ine
I got excited for a moment. Like when you learn Spanish and get most of Italian and Portuguese for free.

I mean, most of the world's population lives in China. So Mandarin would be a good candidate.

More like a quarter.
while China is the second biggest country in terms of population, India has the biggest population. For the majority of the world (>4 billion) to live somewhere, you'd have to take a circle with a diameter from roughly Ulaanbatar to Makassar, and draw it.

i don't think people understand how spanish's utitity matters in the future word in light of the big role it played in the this election and i think that's manifested in vagarious forms of ai like llm's and face detection.

in the end, the fact that the global south is too brown and speaks so "humanly" holds face detection and llm ai's at bay as we descend from this election into the world orwell described in 1984; financed by popularly beloved american oligarchs; and enabled by a two party system through manufactured consent and crowd/social engineering.

and to our new big brother overloads i say this: good morning; i'm pleased to see you again and what would it be my pleasure to do for you today? lol

I excluded Spanish because I am already relatively fluent.
- i saw that and i shared in the hopes of creating discourse that's both relevant to the "interesting" times we've been living in these last few days and add a new perspective for everyone to help encourage engaging with you through your post.

Mandarin

I'm sooooo close with French. I just need to buckle down for like a couple weeks and I'll be fluent I think. I've always heard that's a good one.

I dunno about useful but Japanese is beautiful and I want to learn it