When your first language pops its head up

Various authors and schools have documented L1 interference in English Language Learners. I would like to explore whether L1 interferes more frequently among EFL (out-of-country) or ESL (in-country) learners.  There is also a question about the extent of L2 interference when English is not the L2--I hypothesize false cognates and phonemes (sound substitutions) over phonology (example TBD). 

In the meantime, here's what's available on L1 interference.

Turkish verb tense, articles, and prepositions from https://blog.talk.edu/author/jenny/

Links

https://web.archive.org/web/20210224170739/https://blog.talk.edu/grammar/grammar-errors-common-to-turkish-esl-students/