This relates to pages which are compliant with Western European teletext hardware. Pages in Turkish (such as TRT on Astra 19.2°E), Hebrew, Arabic, etc will appear to misreport their language because they are aimed at teletext hardware with different character sets. There is no support for non-Western languages in either !Teletext or WinTTX.
There are certain (rare) times when the header and the page use different languages. This is supported by the teletext system (and !Teletext under RISC OS) but not by WinTTX. However, for the purposes of the script, the frame language is the language that is returned.