If a word has a vulgar meaning and an informative normal meaning, is it wrong to use? For example, "boi" is a funny way to pronounce "boy," but it can refer to a boyish lesbian or a bisexual with effeminate traits according to Wikipedia. I want to say it as just a funny way to say "boy," without referring to the other definition.
Also, some words contain bad words, such as "cockroach." Some foreign words are bad words in English. Are these wrong?
Are we still sinning by using vulgar words?
We use words to communicate ideas. Thus, it isn't just what you intend to say but also what a reasonable person will think you meant. Therefore, if a listener will assume because of the way you pronounced "boy" that you are calling someone a boyish lesbian, then you giving insult by accusing someone of sinful behavior.
When you used the name "cockroach," everyone knows you are talking about the nasty insect. It's name comes from its Spanish name "cucaracha," which got English-ized in the 1620s to "cockroach." By the way, a male chicken is a "cock" or a "rooster." Because "cock" is connected to male birds, it became a slang word for the male genitals. Therefore, the meaning of the word depends on who you use it in a sentence. It isn't always vulgar.
Foreign words have meaning to speakers of the foreign language. They don't have the same meaning in English, nor do English words have the same meaning in a foreign language. Even if a foreign word sounds similar to a profane word in English, it doesn't make it a bad word.