The third sentence sounds a bit awkward to me. Because it's so obviously referring to a completed action in the past, I'd use the past perfect, like so: "If you had been more vigilant while carrying that precious wallet, you wouldn't have lost it."

I think it's also important to look at the practicalities of this as well. Dialects naturally emerge even within the same country. Language is always changing. In order to keep it static, you'd need someway of ensuring that everyone is communicating with lots of different people. Increasing globalization may make this more possible in the future, but there's no chance in the present.

I have no problem with "approximate" as a verb. It's not exactly an everyday usage; most people would just use "guess", but it's perfectly valid. I've never known of any distinction between "approximate" and "estimate".

On a more grammatical level, "tell" always requires an indirect object. "Say" doesn't. For example, "I told that I'm going to the store" is wrong. "I said that I'm going to the store" is fine. "I told him that I'm going to the store" is fine.

"Their engagement in the conversation increases when they discuss interesting topics. " Fortifies means to increase in strength or durability. The past tense "fortified" doesn't match with the (incorrect) present progressive "they (are) discussing", so I made them both present. You could also keep the past tense and say "engagement in the conversation increased when they were discussing". "Over" isn't used with "discuss" like that. It generally doesn't need a preposition. "If he doesn't comply with my request, I'll complain about him." I've never heard "complain against". "Had he phrased his views on sex crimes properly and appropriately, he wouldn't have to resign." In order to use "then" like that, you need an "if" to go along with it. You could do "If he had phrased... then he wouldn't...". "The presence of awkward phrasing can inhibit effective communication." Saying "a communication" sounds like you're referring to one letter or message. Using the more general "communication" works better here.

Basically, we don't. I've never heard "bespeak" before. It may be a more archaic or antiquated word, but, as a native speaker, I have no idea what it means.

In this case, it means "officially became law". The books, in this case, refer to law books.

"Most of" is used to refer to a subset of a specifically stated group. In "Most of my students", this refers to a subset of students in the group "my students". Compare these phrases: "Most painters" - refers the majority of all painters "Most of the painters in this room" - refers to the majority of the painters in the group of painters in this room. Generally, "most of" is more specific. It specifically states the group you're talking about. Most people love this movie. Most of the people love this movie. You need an article. Most of them are right The fourth sentence in ungrammatical.