Another thing that has happened in several languages, is that w has become m - like in Western Norwegian. The reason is that verb endings have influenced the pronoun - Old Norse "erum vit" ("we are"/"are we") became "eru m(v)it". I expect something similar happened in Slavic and Yiddish.
Some languages, like Sami and Slovenian, have a separate word for "we two" - this map does not show these words.
Also, some languages have separate words for "we (including you)" and "we (but not you)"...