ax-TZ # Not in the registry, but well-formed
fra-Latn # ISO 639 can be 3-letters
fra
fra-FX
abcd-Latn # Language of 4 chars reserved for future use
AaBbCcDd-x-y-any-x # Language of 5-8 chars, registered
zh-Latm-CN # Typo
de-DE-1902 # Wrong variant
fr-shadok # Variant