Also, you refer to the local language as the “Taiwanese dialect.” There are two problems with this. First of all, the difference between a “dialect” and a “language” is a highly political one, but linguistically it is usually based on the concept of “mutual intelligibility.” Since Mandarin and Hoklo are not mutually intelligible, it seems reasonable to refer to them as separate languages. They are, after all, much more distantly related than “languages” like Spanish and Italian. Secondly, the language itself is sometimes referred to as “Taiwanese”, but this has become problematic because the Hakka and Aborigine activists point out that their languages are equally “Taiwanese.” A solution has been to use the term “Hoklo”. You will see that the Taipei Times has begun to adopt this usage.

http://www.taipeitimes.com/News/taiwan/archives/2004/06/08/2003174219

See here for more info:

http://hoklo.org/HokloCulture

Starting to call something a “language” often (but obviously not always) coincides with the rise of nationalist movements, and is thus a political question as you say. Everything I have read so far suggests this is definitely the case with Taiwanese/Hoklo. As such, I’m happy to submit to using the term that insults the least number of people (which is probably a foolish way to measure it since using Hoklo probably insults the nationalistic sentiments of somewhere around a billion Chinese).

While not the case with Taiwanese (except of course for the various movements to establish a writing system for it), sometimes these “languages” are practically invented or mashed together from various idioms, as in Norway’s second official “language” called “ny norsk” or “new norwegian” and Indonesian during Dutch rule etc.