The language-May one recite Birchas Hamazon in English and other languages?
Birchas Hamazon may be recited in any language [that he understands, as will be explained]. Practically, however, the custom is to recite Birchas Hamazon in Lashon Hakodesh, even if he does not understand the language [as will be explained]. [This certainly applies to one who understands Lashon Hakodesh, in which case he is to say it in Lashon Hakodesh, even though it is permitted to say it in any language that he understands.] However, if one does not understand Lashon Hakodesh, it is better to recite it in a language that one understands, despite the custom.
Birchas Hamazon may be recited in any language that he understands. Nonetheless, the custom is to recite it in Lashon Hakodesh. Despite the custom, it remains preferable to recite Birchas Hamazon in a language that one understands, then to say it in Hebrew, if one does not understand the language.
 Admur ibid; Michaber 185:1; Mishneh Sota 32a
The reason: As the verse [Devarim 8:10] states “And he shall bless Hashem etc” from which we learn that it may be recited in any language that one blesses in, as the verse only obligated one to bless Hashem your G-d, and in any language that one understands which he uses to bless Hashem your G-d for the good land that He has given us, he is able to bless. [Admur 185:1; Levush 185; Sota 33a]
 Admur ibid; Rama 199:7; Darkei Moshe 193:1“So is the custom and I have never seen anyone protest it”; Bach 193; Taz 193:2; M”A 193:2; Elya Raba 193:2; Kneses Hagedola 293:2; Olas Tamid 193:2; Kaf Hachaim 193:2
 Kaf Hachaim 185:1 based on Bach 193 and Arizal
The reason: As the Kabalistic intents and unifications are only applicable when recited in Lashon Hakodesh.
 Admur 185:1; See Taz ibid that we rule like the first opinion and only when its either this or nothing that we say one should follow Rashi even initially