1-6 and 12 never came out in the States/Europe but some have translation patches.
They all have translation patches.
FE1 (Dark Dragon and the Blade of Light)-Fully complete.
FE2 (Gaiden)-Fully complete.
FE3 (Mystery of the Emblem)-I haven't played this one, but to my knowledge is fully complete, though the translation is apparently stiff.
FE4 (Genealogy of the Holy War)-Mostly complete, there are a handful of scenes (like two very short ones) that aren't complete. The epilogue crashes, however.
FE5 (Thracia 776)-The worst translation, the entire script is translated but it seems a lot of things were left out/mistranslated. Overall incomplete, there are a few bugs and a lot of menus are garbled completely. There's also quite a bit of garbled text in villages and some boss conversations.
FE6 (The Binding Blade)-Has two complete versions, the original translation and the rewrite translation which fixed the text and added graphical translations that were missing in the first patch.
FE12 (New Mystery of the Emblem)-Complete, and very good. This is a remake of FE3 book two, by the way.