Are you fluent in two or more languages? I’m curious to hear your thoughts about them. Which lanuage is more/less expressive? Which do you like better, and why? Which is easier/harder to master (a tougher question, unless you’re comparing two second languages)? Which makes it more of a pain in the ass to express a simple idea - or easier to express a complex one?
I’m fluent in Dutch, English and Portuguese. I grew up speaking Dutch and English equally, and learned Portuguese because I lived in Brazil. I also speak German, French, Spanish and Romanian but not fluently.
I personally find it easier to speak about certain things in certain languages because the context goes with what I’m trying to say. It’s difficult to find the right words in Dutch or English to describe certain childcare situations I know from Brazil. I find it difficult to talk about nature in Dutch. That’s just personal though, not at all related to the language.
I find, as apparently many people do, that I have slightly different personalities in each language. To me they’re related to the nature or the character of the language. It’s very difficult to explain exactly what it is, though. Portuguese is… very warm, slightly more dramatic, informal. English is also warm, but more in a friendly way, also self-deprecating. Dutch is a little more simple, harsh, more permissive. That’s all wildly over-simplified and horribly stereotypical. It’s not right at all, but I can’t seem to explain it better. There definitely isn’t one that’s objectively more expressive.
I like the feelings of the words you can’t translate. For Dutch people often mention “gezellig”, but IMO “lief” is a much better word. It’s pronounced “leaf” and means sweet or nice or kind. I like that it’s appropriate for everything: you can easily say to your boss that something is “lief” of them, but you can also call your honey your “liefie”, or say you have are in love by saying “liefhebben”.
In Portuguese there is the phrase “ter saudades” for missing someone/something, but it’s different from normal missing. In Portuguese, you remain with something of someone who is gone. That which remains, that’s saudades.
I think those two examples sort of explain what I’m trying to say about the feeling of those two languages: lief is a great word, but it has no drama. It’s simple. Saudades speaks of great drama, deep feelings.
Which is easier to learn depends on what you already speak. English is difficult to learn because the reading doesn’t match the pronunciation, Dutch is very irregular. Portuguese, especially Brazilian Portuguese, is actually pretty simple.
I feel a bit silly having written this, I’m not describing it well at all.
I’m only really fluent in English, but I (at one point) had a working knowledge of Malagasy, can read and write (badly) French, and can understand a tiny bit of Tamil and say some very simple things.
One of the things that fascinates me is the differences in phonology. Tamil, for example, distinguishes between dental and retroflex consonants (those two sets of sounds would be represented by entirely different letters, as I understand it) but doesn’t do much in the way of distinguishing voiced vs. unvoiced or aspirated vs. unaspirated consonants.
I admit to speaking English (American, native speaker), French, German, and Japanese. I grew up in a heavily Hispanic area and understand a lot of Spanish, although I’m not great at generating it. I can read pretty significant amounts of stuff in languages related to the above (Dutch, Swedish/Norwegian, Italian, Portuguese, occasional bits of Chinese), but it depends a lot on context and how much text I have to work with. Street signs maybe not, but Wikipedia articles in Romanian aren’t that bad. One of my contract jobs requires me to work extensively with maps and directions in any one of dozens of languages, so I have a stock of generic place words like ‘pharmacy’ and ‘airport’ and ‘street’ in odd tongues like Turkish and Hungarian and Estonian.
In general, if I can read the script, I can figure out big chunks out on my own. There’s a Russian lesson book on the shelf behind me right now, and it’s not nearly so bad as I feared. It’s just another alphabet and it’s pretty well phonetic, so learning to read isn’t much of an issue. Russian, it turns out, has regular categories of irregular verbs. I pondered the cultural psychology of that and realized it explained a lot about the Soviet era. 
I never feel comfortable in a language until I sound like myself. I have an extensive and sometimes odd vocabulary in my native English, am generally rather dry and drawl a bit, and when I get going I tend to hold forth in a wry mix of formal and informal language. Textbook anything doesn’t cut it. Textbook Japanese felt especially inappropriate to me; Japanese has very gender-segregated ways of speaking, and learning the girl-specific ones also felt ludicrously wrong. I settled on being very bokukko when I speak, which has what I feel are the correct connotations of a girl who is forthright, somewhat bossy, and not easily intimidated.
French is excellent for sarcasm. Because of the way adjectives work and how noun phrases are constructed, you can generate a descriptions of a thing or a situation that are both precise and florid, and deliver them in a matter-of-fact tone of voice. French is generally monotonic, so syllabic stress is purely a matter of emphasis, rather than inherent in a word, and cadence means much when speaking. The Canadians have also accrued a vast collection of useful profanity, from which I borrow freely.
I find German fascinating for its enormous range of accents and dialects. I can hear accents in French and Spanish, but I don’t usually have much trouble understanding them, after a few minutes of adjustment. The spread of German languages baffles me. I’m a fan of a particular figure skater who’s Swiss, from a French-speaking canton. He speaks perfectly good German, but his is formal school-taught Hochdeutsch – albeit with some very Swiss trilled Rs – rather than the local Schweitzerdeutsch. I can understand him when he’s doing things on Swiss TV, and he can (mostly) understand the talk show hosts, but the local dialect is complete hash to me, and I can’t get anything off the interviewers at all. I have to guess what the questions are from his answers.
Japanese is replete with puns and word play. The writing system is complex, and because they threw out all the tone information when they borrowed from Chinese (Chinese was, at one point, the court language there, in much the same way that French used to be the court language for large parts of Europe), there are a lot of homophones. The word kaeru can mean ‘to change’, ‘to return’, or ‘frog’, or it can be a proper name that is spelled like none of the above. It’s possible to help the reader with the pronunciation of unfamiliar words with small phonetic characters called furigana, printed above or to the right of the characters they give a guide for, but there’s no rule that says the reading given by furigana has to bear any resemblance to the way those kanji would normally be read. It is entirely possible to smash together a construct that means Super Ultra Master Technical Blueprints For All The Cosmos And Beyond, and to tell the reader it’s read e, ‘picture/painting’. It’s often used to give subtext in manga or the printed song lyrics you find in CD inserts. It’s amusingly snarky to look in the booklet and find the phrase the singer pronounces ii otoko (‘nice man’) is spelled with the characters that normally say kyuuketsujin (‘vampire’).