What is the ruling of the Shari'a regarding not advising non-practicing Muslims in a foreign work environment, given language weakness and the presence of reprehensible acts not directed at me, and am I sinful because of that?

The hadith with the mentioned wording is weak, but the correct wording is: "Let not the fear of people prevent any of you from speaking the truth when he knows it." And with the wording: "Indeed, Allah will ask His servant on the Day of Resurrection: 'What prevented you from denouncing the evil when you saw it?'"

These two hadiths are interpreted to mean that the only impediment to denouncing evil is mere awe, not a fear that would excuse one from denouncing it.

The fundamental principle regarding the denunciation of evil is that it is a collective obligation (fard kifaya) and becomes an individual obligation (fard ayn) upon whoever else does not undertake it. The evil that is to be denounced is the manifest evil. So, if you see a manifest evil in your workplace, such as a female employee displaying herself improperly (tabarruj) or listening to music, and no one else is denouncing it, and you do not fear harm, then strive to denounce it and advise with gentleness and wisdom.