"Yo solo hablo una lengua."
Translation:I only speak one language.
It's just teaching you a different word, but you should stick to idioma since it is more natural.
My sense is that idioma is more formal and lengua is more common. I use idioma strictly to avoid confusion with that thing in the mouth---if only others felt the same way!
I wish DL would tell us about the differences in shades of meaning between words they translate the same.
07/09/18. It would be "un idioma." Don't let the "-a" ending on this one trip you up (it's just one of the exceptions to the noun gender rules).
"Tongue" is used in English in the same manner as in Spanish. "I only speak one tongue" should be accepted. (reported)
Weird that it isn't accepted on this question. I translated lenguas as tongues on another and it said it was fine.
Sorry, but it is necessary to have an accent over the 'o' if you're going to use 'solo' as an adverb. Otherwise, it is an adjective, meaning 'alone'