Loaded terms in free software

This is unrealistic. There are basically two options here:

1. The text will be translated (rare for source code, common for just about everything that a non-programmer might read or write).
2. The text will not be translated, and non-English speakers have to either learn English or give up on reading it. (Or replace "English" with whatever language it was written in.)

In case (1), the translator is responsible for selecting appropriate words in the target language. If a literal translation would be rude, they are expected to rephrase as necessary. This is a completely standard thing for translators to do; if you've ever read anything translated into English, somebody probably had to modify or rewrite some idiom, joke, or other cultural reference to fit the English language, and the same happens in reverse.

For example, many languages which are not English have a plural second person ("you") pronoun. In English, most plural second person pronouns are considered slang or colloquial (y'all, yinz, youse, etc.), but in many other languages, this is a standard word that anyone might use in any context. Similarly, many other languages distinguish between formal and informal "you," but English doesn't. Translators need to smooth out both of those differences, as well as many others. You might introduce honorifics (Mr., Ms., etc.) or other courtesy markers (sir, ma'am, etc.) for the formal "you" and discourtesy markers (e.g. addressing by first name, use of unrelated slang, etc.) for the informal "you." Plural "you" might be translated as "you guys," or a similar phrase, or it might just be written as "you" if the plural can be inferred from context.

(Incidentally, this is why translation is widely regarded as an AI-complete problem. You don't just have to parse and understand the literal meaning of each word, nor even the grammar of the entire sentence. You have to understand the overall effect that each sentence has on the reader, and endeavor to recreate that effect as closely as possible.)

In case (2), the non-English speaker is unlikely to have slang associations with the English phrase, because to them, English is a foreign language. If they do have such associations, they are likely trying to translate word-for-word and reassemble the sentence in their native tongue, which is usually not a very effective way of reading a foreign language. Of course, it's not ideal to tell these people "Go study English harder and you won't make that mistake," but there are limits of accommodation. If someone frequently misinterprets standard English as slang or colloquialisms that don't exist within the English-speaking community, then further study may be the only way around the problem.