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src/content/docs/topics/computing/lang_tag.md

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+---
+title: Language Tagging
+sidebar:
+    order: 2330
+---
+
+Focus on how apps should handle language tags
+
+## Published API for applications
+
+The main thing to be aware of is that the file is available here: [https://ldml.api.sil.org/langtags.json](https://ldml.api.sil.org/langtags.json)
+
+When an sldr file is desired, use the minimal tagset: [https://ldml.api.sil.org/srq](https://ldml.api.sil.org/srq) and the `srq.xml` file would be downloaded.
+

src/content/docs/topics/writingsystems/lang_tag.md

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+---
+title: Language Tagging
+sidebar:
+    order: 1410
+---
+
+What is a language tag? See docs in languages repo
+
+SIL’s `langtags.json` file resides in the a langtags repo. Information on making a maximal and minimal language tag is derived from various sources.
+
+- `langtags.csv` is manually maintained. We have close cooperation with the Ethnologue script editor. Any new information on writing systems for a particular language in the Ethnologue is passed on to be included in the `langtags.csv` file and vice-versa.
+- [IANA Language Subtag Registry](https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry) - this file is placed in [sldrtool repo](https://github.com/silnrsi/sldrtools) and is available [here](https://github.com/silnrsi/sldrtools/blob/master/lib/sldr/language-subtag-registry.txt). (LE:This makes no sense to me why it would not be in the langtags repo.)
+   - ISO 639-1
+   - [ISO 639-3](https://iso639-3.sil.org/) (no files are directly used, IANA incorporates the changes)
+- [Ethnologue](https://www.ethnologue.com/codes/) (`LanguageIndex.tab` is renamed `langindex.tab` and placed in `langtags/source`
+   - `autonyms.csv` is from the Ethnologue, but it is not publicly available for download from the Ethnologue.
+- [ISO 15924](https://unicode.org/iso15924/iso15924-codes.html) script codes are used. However, no downloaded files are used, the information is manually added to `langtags.csv`.
+   - A few of the script codes may need to be described.
+     - Zyyy is used for when the script is unknown
+     - Zxxx is used for Sign languages
+     - Zzzz is used for unencoded scripts. In those cases a subtag indicates the script name
+- ISO 3166-1 alpha-2 country codes are used. However, these are derived from the Ethnologue `LanguageIndex.tab` file which includes all the regions.
+- We are in the process of incorporating [ROLV (Registry of Language Varieties) codes](https://hisregistries.org/rolv/). At this point these would be processed as private subtags.
+- During the build process of `langtags.json`, the sldr files are also used for testing purposes. Any language tags that are used in the sldr files should be added to `langtags.csv`. If the sldr file is incorrect, it should be corrected.