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How to prevent a colleague introducing extreme complexity and abstraction?

I am having a very difficult time because my colleague seems to exhibit

1) Premature/Unnecesary optimization efforts
2) Premature deduplication with questionable abstractions
3) Inventing general purpose solutions for speculative potential future features
4) Opting for incidental complexity

How do I fight this when he also exhibits having a language barrier with louzy english?