[tannenfreund87]

I grew up in southern Germany, speaking the local dialect. As a young adult, I thought I could speak accent free German. I couldn't have been more wrong. Many people in Hamburg and Berlin rightfully guessed that I'm from Bavaria. Closely related languages and dialects exist in a continuum ((Max Weinreich: "a language is a dialect with an army an a navy"). Many people in Ukraine spoke and speak "surzhyk", depending on the political climate, they could claim to speak Russian or Ukrainian. Then Russian and Ukrainian, together with Belarusian form a dialect continuum. You can easily understand you neighboring village, but it gets harder and harder, the further you are apart until there's very little mutual intelligibility.

[vkazanov]

I grew up in the east of lithuania, mostly hearing polish and russian in my early years, and then also lithuanian to a smaller degree.

I eventually managed to separate the languages proper but I clearly see how the languages are are not a discrete classification.

Like, lithuanian polish and lithuanian russian are similar, but polish polish is further away phonetically.

Lithuanian has weird phonetics but the underlying grammar is very close to slavic languages.

English is much further away on the spectrum but why are sentence intonations (irony , question, etc) are still strangely compatible with languages from other branches of the language tree..?

Conclusion: strict language separation is a political construct not a natural thing.