There is a question posted in the German community forum about the job requirements for the Aircraft mechanic/machinist/technician in German airlines Lufthansa, particularly regarding the English language proficiency.
User ramay1418, an expert in aircrafts, provided this detailed answer (and also recommended TrackTest, thanks for that :-):
(loosely translated in English)
Your English should be relatively good. You should be at the level B1 or even B2 based on EU CEFR standard (Common European Framework of Reference for Languages). Like in real life, a better level is naturally always better :-).