wow. lots of questions! and i'd like to answer them since... i really like furuba and i have lots of the volumes in french! so here i go!! ^-^
kyo has a language problem initially, and so does one of tohru's friends arisa uotani (but it's more... rare). firstly the comic is not THAT bad, he usually just says the word "d*mn" alot, and i think once in a while he decides to say "sh*t" but this is part of the humour (because no matter how big he tries to sound, no one cares.
poor kyo) in my experience when i go to read something translated into english, i find that they have added even MORE 'words', but since i am not interested in the english version, i'll just say it depends on the maturity level of your child and what YOU think is appropriate for him/her.
it also should be mentioned that the characters in this comic are not christian. most of the time it doesn't matter, and it's very mild, but you should just keep this in mind, like in most cartoons. for example, once shiguré says; "i don't know what's going to happen. i don't even think our gods know.." and tohru saying "i went to the temple to pray that they get along better... but it doesn't seem to have worked" just little things like that. (because... well... the whole series is based on the chinese zodiac. so this should be expected.) also you will find out that a character in the series represents the "god" that made the chinese zodiac, however to my knowledge he is not granted any special powers, worship, and other "divine" thingies... he's just a guy, and infact, has very weak health.
the comic is still ongoing. i think the 5th volume has come out in english, the ninth has come out in french, the 12th just came out in korean, and finally, the 13th came out in japan. it hasn't ended and tohru has not gone with anyone to my knowledge. i don't think the anime will be continued.
I don't really have favourite characters. they are all so cute or so funny. kyo and yuki are so different but the same too... i hope one day they get along (i kind of know why kyo hates yuki but-- that would be too much of a spoiler!) i like both kyo and yuki equally. i love ayamé and shiguré, they are so funny, and when they're together with hatori they're lethal!! DYING OF LAUGHTER~!
ugh, i'm going to end by gushing here, but i really hope yuki tells tohru he loves her. or kyo finally accepts kagura! i hope kyo realizes that everything he wants in tohru, he is freely offered by kagura. and just to spoil you guys a bit... kyo hugs kagura in one of the later books.
p.s. YAY for tohru and yuki!! thank you blue elf!!!