i actually got heartgold in french as a valentine's present from a friend of mine a few years ago, to help with my french skills.
my eyes rolled back into my head as i tried to read it. i could understand maybe half of it at best. i put it down for a while [~four months-ish] after the second gym and came back when i'd taken more lessons [both formal and online], and i breezed through it like nobody's business, probably with at least 90% comprehension. it helps if you've played the game before because you have additional context to look into if it doesn't come to you right away. i asked the same friend which language i should play y in, and boy am i glad did i pick french. it is /so/ easy to find foreign 'mons for masuda/dex entries, and it's still a great tool for learning.
battling isn't too difficult, in my opinion, because even if you don't recall what the name of the move itself means, you can read the description and check its type/pp/etc and you should be able to figure it out. when npcs mention a certain species or move and you can't check a reference it could be annoying, though.
however, i wouldn't say that these games are really things that you just plop into without knowing any of the language to begin with. i mean, you
could, nobody's stopping you, but personally, i find stumbling like a toddler lingually like that rather stressful, especially [but not only] in more demanding real life situations. the vocab in the game is made for kids, but it's not made for babies - they plan for about six-to-eight-year-olds at the very least to read it, so keep that in mind. i'd take a few lessons on
duolingo [it's free, and set up in a game format] to set you up with basic syntax and such first. looking things up in the dictionary is acceptable, sure, but it's tedious, and better if you already know some to start you up.
i'd very much encourage it, though. i'm all for people learning languages, especially in a fun way like learning with pokemon. heck, i'm sure enough people in this thread learned to read in
english with pokemon, or at least they were helped by it [i know i was, even though i started when i was about nine, later than most people], so it's definitely a cool way to learn.
[my sibling got a y game but stole my ds to play it and thus accidentally set his game to "español" at the language select screen due to my ds being in spanish at the time {ps: change your console language to the language you pick, too, if you can - i find it really helps}, so i've been thinking about improving my spanish that way since he can't play it whether i touch it or not... can't find the cart, though]
also, the foreign names of some mons are /great/. take lickitung - in german, it's "shlurp," which is funny as hell. pidgeot also took a level in badass for his magical baguette audience [that's french, by the way], and so took the name "roucarnage," - snatchin' yo' people up.
sorry for the essay and a potential necro [it's still on the front page, though, does that count as a necro?] but either way, this project deserves more attention!