I watched a video on the Second Commandment (Third for Jews, Second for Catholics) and what I got from it is this:
If someone were to say, “God, did I have a bad day at work today,” then a former interpretation of this Commandment would’ve told us that this person has mortally sinned. However, according to Dennis Prager of Prager University, the Second (being careful not to say Third) Commandment does not say, “Don’t TAKE the name of the Lord your God in vain.” The original Hebrew translation reads, “Do not CARRY the name of the Lord your God in vain.”
So, I’d think that saying something like “Oh my God” outside of prayer would be venial sin, but this is just an assumption. I do know, however, that the original translation entails doing evil acts in God’s name. Take the actions of Al Qaeda, the terrorist Islamic group responsible for 9/11. If they had the same Ten Commandments that we do, then this would be what the Commandment concretely prohibits, since they hijacked and crashed 3 planes in the name of Allah. Assuming that Islam and Catholicism are, for the most part, synonymous, then this should not be the approach that Muslims take to convert.
In short, all of the situations above are venial sin at the very least, the second being mortal sin for sure. But, it is simply a mistranslation that prevents us from fully understanding this Commandment.