Regarding the second half, I find that problematic. Sometimes it's very clear to me that English is not someone's first language, and you can often tell what is

Regarding the second half, I find that problematic. Sometimes it's very clear to me that English is not someone's first language, and you can often tell what is by the mistakes they are making (for example, "I have been working here since 3 years" is a common mistake by native German speakers, as it's a direct translation of the equivalent phrase in German). In that situation I find many people are appreciative of stylistic notes, but it's hard to pull off without looking like a grammar [fascist].