Apple's search API documents specify:
lang =
The language, English or Japanese, you want to use when returning search results. Specify the language using the five-letter codename. For example: en_us.
The default is en_us (English).
examples: en_us, ja_jp
However, I cannot find this 5 letter standard codename. Are they just expecting a ISO 639-1 Code concatenated with a 2 letter country code?
Has anybody ran into this issue before?