First of all, welcome and you've asked a number of good questions. For starters, translating any written word to another language is a perilous task. Even between two languages as similar (at least in terms of word similarity if not in structure) as English and French, there are problems. Poetry is even more difficult and poetry that is full of word imagery is like trying to make lobster thermidor from a pile of hay and a crowbar. If you understood that, then read on. I studied French some 40 years ago and know something of the language, but perhaps
Black Swan can help here as she is from Québec and not only speaks great English, is something of a Buk scholar as well.
Before I get to your questions, Buk's poetry went through several phases. Lots of imagery at the beginning that eventually became a far more direct approach later. In the late '60s/early '70s, when many of the poems in Mockingbird were written, he still had quite a bit of imagery - not abstract imagery like early on, but more like stream-of consciousness imagery. So translating that is difficult.
As to your questions:
but i imagine
war being swine mob being swine
I don't get "swine" as a verb. usually it means pigs or bastards, right ?
and also in that case, what is "mob" (the crowd ?)
"Swine" is being used as a noun in both cases (pig is a synonym, although bastard is not a bad translation). What Buk seems to be getting at is that the war itself is filthy, but the mob (yes, crowd is a synonym, although mob has a connotation of being more disorderly) who are all gung-ho about the war as just as filthy as war itself.
hoping he'll chitter
and peep some pink
back into white elbows.
not a clue about "peep some pink ..." what does that mean ? is it an expression ?
It's hard to say, but reading the poem, it would seem to be about the changing of the season from Winter (such as they get in LA) to summer and the bird he is referring to (chittering being something a bird does when ruffling his feathers, so to speak) is hoping to get some color back into his body - not so much literally as much as "becoming alive" again in warmer weather. At least, that's what I take from the lines.
lift high their fish-green beer
never heard of fish-green beer ... is it a brand ? or some expression ?
Not a brand but perhaps a reference to the swill some folks drink on St. Patrick's day, but more likely just a term for cheap beer. Or beer being drunk by men who don't think as much as Buk does.
I itch from the slush of the Philippines
to the eye of the minnow.
I get the main idea, but not exactly. any help on this ? what's "slush" in here ? a liquid, like some kind of beer?
Not beer, I don't think, but I'm stumped by this line. Perhaps something to do with WWII and how the Phillippines were tangentially involved.
rough-tit crab
I get the rough crab, but why is there -tit ? is it adding something ?
Just a little embellishment to the image, I think. Obviously crabs don't have tits (shame, really) but sometimes he just tosses in a "street-lingo" type of thing to keep it real. Even if it isn't.