There is no arbitrary skill ceiling, but I think you underestimate how much long term immersion matters. I&#x27;ve lived in the UK fo 16 years. I started learning English at 7 and in school from I was 10, and used it daily from about 14 (I&#x27;m 41 this year).<p>Yet living in the UK I still regularly come across idioms and words that are second nature to people who grew up here that I haven&#x27;t heard before.<p>E.g. I have a six year old son in primary school here, and through that now come into contact with expressions that people that grew up here experienced in primary school, and that most of them may not have used since then but are aware of, but that are totally new to me.<p>And I think this matters much more when translating into a target language than in the source language. While you may fail to recognise some idioms, it is easier to recognise something that sounds odd or words you don&#x27;t know, than to recognise that you are missing vocabulary you didn&#x27;t think was necessary (e.g. the word &quot;mufti&quot; was entirely new to me when my son started school; prior having him in school, if I was asked to translate anything about coming in out of school uniform, I&#x27;d have never known I was &quot;missing&quot; a word, and would have used a longer expression instead).