From Middle English outland, outlond, from Old English ūtland, from Proto-Germanic *ūtlandą, equivalent to out- + land. Cognate to Dutch uitland, Afrikaans uitland, German Ausland, Danish udland.
The use in the phrase "outland German" is influenced by (or is a calque of) the German cognate of the same meaning, Auslandsdeutsche (see Ausland). The use in the phrase "outland Chinese" is influenced by (or is a calque of) the Chinese term of the same meaning, 華僑 / 华侨 (huáqiáo).