I've had lots of occasions lately to notice the different way that languages feel. My kids have been learning a bit of French, and there's always some Japanese floating around my house, and often enough I find myself commenting on other linguistic sources, like when I'm reading my son's dinosaur book and come across Tuojiangosaurus. To him it's a dinosaur name that's tricky to say. To me, it screams "Chinese!"
Part of the feel of a language comes from its inventory of sounds. In German, the very existence of sounds like the "ch" in "ich" changes the feel of the language, where in Chinese you get sound combinations, complex syllables, and tones to boot. But if you look at just the sound inventory for a language you can miss things, because some languages have similar inventories - like, for example, Spanish and Japanese. When I was living in a foreigners' dormitory in Tokyo with 360 students from 60 different countries, we all noticed there was a certain advantage for the Spanish speakers in pronunciation. Still, sounds alone aren't enough.
Intonation is a huge part of the feel of language - a part that I don't see described in fiction as often as I'd like.
English has syllable stress, where one syllable of a word tends to be louder and higher in pitch than the others; this influences things like the aspiration of consonants, which is when a sound like "t" is followed by extra exhalation almost like "h." It also makes for all the metrical patterns we see in poetry, and changes the feel of a sentence drastically. I know I'm always looking out for a good metrical feel when I write, even though I don't count out syllables when I do it. It influences what they call "flow."
Neither French nor Japanese has syllable stress. I haven't studied French intonation in as much depth as Japanese, but effectively, in French there isn't any syllable that sticks out in both loudness and pitch, though I do notice a slight rise in pitch at the ends of sentences. Japanese has a pattern of pitch accent which means that there's no difference in loudness, but each syllable (mora, for sticklers) has a pitch value which is relatively higher or lower, so that the speech tends to flow along, alternating between the two.
Here's an interesting trivia tidbit about English speakers learning French and Japanese: even when they're able to produce all of the right sounds, they can have trouble taking the stress out of their speech. This makes for a rather interesting accent, because it's easy to tell that they don't sound native, but hard to pinpoint exactly the source of the issue because technically all the sounds are correct.
I know I've mentioned mouth shape before, but I'll mention it again. French to me is like calisthenics for the lips, because of the variability of the different sounds and mouth positions - and without that, it wouldn't sound as French. Japanese always feels to me like it should be uttered with a faint smile on the lips, because it has much less range in mouth position. Even the Japanese "u" is un-rounded. I literally used to get my Japanese classes to pronounce words better by asking them to "smile when you say that."
Then there are the intangibles. Where do I get the feeling that French and English are playful languages? Maybe from all the puns I've heard in each? I know I get a feeling that Japanese is a graceful language, but I don't ever get the same sense of playfulness. But maybe it's just because I've been in all the wrong language-speaking situations. I could easily imagine a situation where a language-learner thought the language had no humor, just because he'd never been in the right context to hear it.
Languages have such a vast range of use contexts that it's hard to capture them in their entirety. ESL teachers in the US know that it's perfectly possible for someone to be great at playground talk, but to struggle with English for academic purposes. I know from experience that having a good ear for accents and a lot of conversational experience isn't enough to make me feel comfortable when I need to get medical help in either France or Japan. That's a specialized area of vocabulary that I've hardly touched.
In Japanese you also have the issue of formal and casual language, which are used in different contexts. Because of the amount of formal language I've studied, I feel less comfortable using casual forms, and it has the odd effect of making me feel less comfortable speaking Japanese to my kids than French. I don't want to talk to my kids as if they're colleagues or fellow students! It just feels weird.
Those are my thoughts for this evening. I've decided to go ahead with my plan to take a closer look at some characters from books, and how they feel grounded in culture and belief systems. I've been putting together a pile of books, and I hope to get started with that in the next day or two.