I can understand your approach, Zoran. Learning slang too early in the language learning process can be overwhelming and counterproductive, especially if you have to use the language for business or school. It's important to focus on building a strong foundation of the language, including vocabulary and grammar, before delving into more informal expressions like slang.

However, as you pointed out, exposure to the language over time will naturally lead to the acquisition of slang words and phrases. As we become more comfortable with the language and start interacting with native speakers, we will naturally pick up on the nuances and colloquialisms of the language.

In my own experience learning languages, I've found that slang is often context-dependent and can vary greatly depending on the region or social group. This makes it even more important to focus on building a strong foundation of the language first, and then gradually incorporating slang as we gain more exposure and experience.

For example in Japan I have a lot of business, but they also really love slang when we are drinking after hours with business friends.

I agree, especially if you do not want to sound like a poor immigrant who's only option was to learn the language from the street. Being as well spoken as possible in my new language is my top priority. Concentrating on slang can also leave one in a time warp,especially if one does not keep up with all the new words and phrases. We may end up speaking like Austin Powers!