sdd-1 being kind of useless as star ocean is already playable with a patch
Yes, but is it possible to apply a translation to the patched rom ?
Or maybe apply the patch to a translated rom ?
I don't think it is possible, but I don't try yet.
If it is impossible, the S-DD1 compatibility can be usefull for non english peoples 
Yeah, exactly. The "sdd1 support is dum lol" contingent is pretty sizeable, but short-sighted on some levels, as you correctly point out, and downright dickish on others. I find "street figher alpa 2 is a bad game and nobody shud ever be able to play it on sd2snes" to not be a very compelling argument, to say the least.
Kinda blows my mind that some people are perfectly content with the idea of SD2SNES firmware development stopping altogether when support reaches 1,253 games out of the 1,254 released in NA and PAL territories. I figured this nonsense would stop when SA-1 was functional and only S-DD1 and SPC7110 remained, but I guess not.
At this point, I won't be surprised if magno (or somebody else) puts out a working S-DD1 core, and people are STILL going "mango u ruined sd2snes delete teh sdd1 core now it sux lol".