Wales, Wallonia and Wallachia share one name: "foreigners".
Germanic peoples called their Romance- or Celtic-speaking neighbours *walhaz, derived from the Celtic tribe of the Volcae. The word travelled: the Anglo-Saxons called the Britons "Welsh", the Dutch call Walloons "Waals", and in the east Romanians became "Wallachians" and "Vlachs". Swiss still say "Welsch" for French-speaking Switzerland, and Lake Walen marks an old language border.
Useful: If "wal-" or "welsch" is in a name, someone once spoke a language there that the Germanic tribes didn't understand.
Source: en.wikipedia.org