Most opera singers are are proficient (if not fluent) in 3-4 languages; typically Italian, German, French and English. Many European artists are fluent in more. My younger daughter sings opera and took three weeks of diction lessons last year before performing
Janáček's The Cunning Little Vixen in Czech.
Most pop artists that sing in a non-native language simply learn (read) the words phonetically.
Most pop artists that sing in a non-native language simply learn (read) the words phonetically.