Minimum Criteria For Language Support (I18N)
Support in Unicode
Languages may have one or more scripts for writing purpose. Atleast one of such scripts should be encoded in Unicode.
Locale Definition in glibc
A completely filled locale file for the language has to be present in glibc and installed at /usr/share/i18n/locales/ .
A Unicode Font
Atleast one font that covers the Unicode range for the given script (of the language) which is usable1 must be present.
Shaping engines (e.g. Pango, Qt, ICU etc.) should support the script grammer for the script of given language (at least Pango).
There should be at least one simple method for inputing text in the given language. As SCIM is the current default input method, there should be support for the language in SCIM, preferably at least one m17n keymap and any additional processing (modules) required for the language specific features.
Entry in comps
The comps file for a given distro should have the entry for the language support which lists all the necessary packages to be included that satisfy at least Font and Input Methods requirements.
Entry in system-config-languages
User should be able to select the given language from system-config-languages utility.