ADJ

first, native
She grew up in Spain, so her first language is Spanish
foreign, second
How many foreign languages does she speak? the teaching of English as a second language
original
Most local cinemas show films in the original language, with German subtitles
source, target (both technical)
ancient, classical, dead
Latin is a dead language
modern
common, shared
indigenous, local
official
Belgium has two official languages
national
Portuguese is the national language of Brazil
international
minority
Some minority languages are dying out
spoken, written
She could speak some Chinese, but never studied the written language
colloquial, everyday, informal
formal
flowery, literary, poetic
racist, sexist
sign
Not all deaf people use sign language
body, non-verbal
You could tell from his body language that he was very embarrassed
legal, technical, etc.
computer, programming

VERB + LANGUAGE

speak
understand
use
learn, study
master
be couched in, be expressed in
enrich
idiomatic expressions that enrich the language

LANGUAGE + NOUN

acquisition, learning
new methods of language learning
course, lesson

PREP

in … ~
His letter was couched in very formal language

PHRASES

command/knowledge/mastery of (a) language
Her command of language is very advanced for a six-year-old
use of language
The writer's use of language reflects the personality of each character

ADJ

bad, crude, foul, obscene, offensive, strong
using foul language

VERB + LANGUAGE

use
mind, watch
The referee warned the players to mind their language