1. First make sure that you do Update Language/Script/Region Subtags first
2. Run GenerateLikelySubtags with VM argument -DCLDR_DIR set to your cldr directory to generate the likely subtag data AND the default content locales.
   1. If you are trying to debug, add the VM argument -DGenerateLikelySubtagsDebug
3. Input data:
   1. Data comes from territory/language information in supplemental data.
      1. However, it is supplemented by LANGUAGE_OVERRIDES in GenerateLikelySubtags.java
         1. If there is no territory/language information in supplemental data for a language, add it to LANGUAGE_OVERRIDES.
         2. If the mapping changes when it shouldn’t (there are some special cases), add to LANGUAGE_OVERRIDES.
4. Output:
   1. Creates {CLDR_DIR}/../Generated/cldr/supplemental/likelySubtags.xml and {CLDR_DIR}/../Generated/cldr/supplemental/supplementalMetadata.xml
   2. Diff with {CLDR_DIR}/common/supplemental/likelySubtags.xml and {CLDR_DIR}/common/supplemental/supplementalMetadata.xml
   3. Be very careful to diff everything and check for errors.
      1. Watch especially for backwards incompatible changes; that is, changes rather than just additions.
      2. Look at the above to handle that with LANGUAGE_OVERRIDES.
   4. Run tests, fix input data, and iterate as necessary.
      1. Copy into the svn workspace and commit.

Updating langtags.json

langtags.json is used as an additional source for likely subtag information.

To update:

• Go to https://github.com/silnrsi/langtags/releases/latest and find the latest release
• Download langtags.json and copy it to ./tools/cldr-code/src/main/resources/org/unicode/cldr/util/data/external/langtags.json
• Check git diff - if there’s no change, you’re done.
• Re-run GenerateLikelySubtags (just as in the above section)
• If there are no changes to likelySubtags.xml, then just check in langtags.json and note that.
• diff the results, run tests, check in, etc. (see above)
• Note: You can use the --json command line option to GenerateLikelySubtags to get detailed warnings about langtags.json

Example update to likelySubtags.xml: (note the origin= attribute)

+               <likelySubtag from="aci" to="aci_Latn_IN" origin="sil1"/>               <!--Aka-Cari‧?‧?        ➡ Aka-Cari‧Latin‧India-->
+               <likelySubtag from="ack" to="ack_Latn_IN" origin="sil1"/>               <!--Aka-Kora‧?‧?        ➡ Aka-Kora‧Latin‧India-->
+               <likelySubtag from="acl" to="acl_Latn_IN" origin="sil1"/>               <!--Akar-Bale‧?‧?       ➡ Akar-Bale‧Latin‧India-->