Old English tunge "organ of speech, speech, language," from Proto-Germanic *tungon (cf. Old Saxon and Old Norse tunga, Old Frisian tunge, Middle Dutch tonghe, Dutch tong, Old High German zunga, German Zunge, Gothic tuggo), from PIE *dnghwa- (cf. Latin lingua "tongue, speech, language," from Old Latin dingua; Old Irish tenge, Welsh tafod, Lithuanian liezuvis, Old Church Slavonic jezyku).
For substitution of -o- for -u-, see come. The spelling of the ending of the word apparently is a 14c. attempt to indicate proper pronunciation, but the result is "neither etymological nor phonetic, and is only in a very small degree historical" [OED]. Meaning "foreign language" is from 1530s. Tongue-tied is first recorded 1520s.