If the teacher of a foreign or second language keeps learning and acquiring that target language, if he perseveres learning himself, for example one or two words or phrases each day, he will be making up a massive tank of vocabulary that will be brought up while using that language; even he will recall words he thought he didn’t know.
He’s creating the sense of the language, by means of which he’s making the foreign or second language his own second language!
Those words and phrases will be brought up unconsciously, whilst he’s writing for instance. They just come to mind!
By the way I would advise foreign language teachers should aim at C2 level, within the Common European Framework – it’s the highest level, out of six ones. / Photo from: sg theasianparent com