Barthandelus Japanese name

[The Summoner of Leviathan]

His japanese name is "Barutoanderusu" - "Garensu Daisuri".

Does that mean anything in particular? How does it translate to English?

That's just his japanese name. You cannot say how it will be translated generally because it is just a name. Often it depend on how you pronounce the english letter so Crisis Core's "Ka-n-se-ru[/b]" is translated "Kunsel", et cetera, but you cannot say you translate it all the same way, because Katakana are used for...yeah, names like I have explained. "Fuainaru Fuantashi - Final Fantasy".

I for example have called "Barthandelus" "Baltoanders" before he had his american/european translation. I thought the would translate him like that. Or "Gurenth Dysry".

Technically ファイナルファンタシ is "Fainaru Fantashi". For it to be "Fuainaru Fuantashi", it'd be written フアナルフアンタシ. The difference is slight, but significant in pronunciation. ファ is read as "fa" and フア is "fua". ファ (fa)、フィ (fi)、フェ (fe)、フォ (fo)、ヴァ (va)、ヴィ (vi)、ヴェ (ve)、ヴォ (vo)、and ティ (ti) are commonly used in katakana to represent sounds not native to the Japanese language (in this case "f" and "v", though at times for "v" they will use the "b" sound)

According to Wikipedia:

Barthandelus (バルトアンデルス, Barutoanderusu?, Baldanders in Japanese version)

Apparently, Baldanders is a Germanic creature that represents the constant changing of both nature and society and is a shapeshifter.