ICU-23056 initial ICU 78 download page

See #3687

Author: markusicu

docs/download/78.md

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+---
+layout: default
+title: ICU 78
+nav_order: 898
+has_children: false
+parent: Downloading ICU
+---
+
+<!--
+© 2025 and later: Unicode, Inc. and others.
+License & terms of use: http://www.unicode.org/copyright.html
+-->
+
+# ICU 78
+
+ICU is the [premier library for software internationalization](https://icu.unicode.org/#h.i33fakvpjb7o),
+used by a [wide array of companies and organizations](https://icu.unicode.org/#h.f9qwubthqabj).
+
+## Draft page
+
+**This is an early draft of the ICU 78 download page. Nothing is published yet.**
+
+## Release Overview
+
+* Download: TODO [releases/tag/release-78-1](https://github.com/unicode-org/icu/releases/tag/release-78-1)
+* TODO [Maven: com.ibm.icu / icu4j / version 78.1](https://mvnrepository.com/artifact/com.ibm.icu/icu4j/78.1)
+
+ICU 78 updates to
+[Unicode 17](https://www.unicode.org/versions/Unicode17.0.0/)
+([blog](https://blog.unicode.org/2025/09/unicode-170-release-announcement.html)),
+including new characters and scripts, emoji, collation & IDNA changes, and corresponding APIs and implementations.
+
+It also updates to
+[CLDR 48](https://cldr.unicode.org/downloads/cldr-48)
+([alpha blog](https://blog.unicode.org/2025/09/unicode-cldr-48-alpha-available-for.html))
+locale data with new locales, and various additions and corrections.
+
+TODO: High-level summary
+
+ICU 78 and CLDR 48 are major releases, including a new version of Unicode and major locale data improvements.
+
+TODO status update:
+The Java technology preview implementation of the CLDR MessageFormat 2.0 specification has been updated to incorporate the
+[CLDR 46.1 spec](https://www.unicode.org/reports/tr35/tr35-74/tr35-messageFormat.html)
+plus most but not all of the CLDR 47 changes.
+
+TODO status update:
+The C++ technology preview implementation of MessageFormat 2.0 is not yet quite up to date with CLDR 46.1.
+
+For more details, including migration issues, see below.
+
+Please use the [icu-support mailing list](https://icu.unicode.org/contacts) and/or [find/submit error reports](https://icu.unicode.org/bugs).
+
+### Attention: Future Changes
+
+TODO status update:
+Beginning with ICU 78 (2025-oct):
+
+1. We want to move the minimum required Java version from Java 8 to Java 11.
+   This is a significant, useful update in terms of the Java language and
+   standard library, and simplifies ICU tooling which currently uses
+   a mix of Java 8 and Java 11.
+   Note that [Android desugaring](https://developer.android.com/studio/write/java11-default-support-table)
+   supports at least Java 11 since late 2023.\
+   See [ICU-23072](https://unicode-org.atlassian.net/browse/ICU-23072)
+   where you can provide comments.
+2. We are planning to remove the
+   [ICU4J Locale Service Provider](../userguide/icu4j/locale-service-provider.md)
+   ([Maven: com.ibm.icu / icu4j-localespi / version 77.1](https://mvnrepository.com/artifact/com.ibm.icu/icu4j-localespi/77.1)).
+   It is much less useful than when we added it, has very low usage,
+   needs work for newer Java versions, and complicates ICU4J development.\
+   See [ICU-23071](https://unicode-org.atlassian.net/browse/ICU-23071)
+   where you can provide comments.
+
+### Version Number
+
+The initial release has library version number 78.1.
+
+* Release date: 2025-10-TODO
+  * [List of tickets fixed in ICU 78](https://unicode-org.atlassian.net/issues/?jql=project%20%3D%20ICU%20AND%20status%20%3D%20Done%20AND%20resolution%20in%20%28Fixed%2C%20%22Fixed%20by%20Other%20Ticket%22%29%20AND%20fixVersion%20%3D%2078.1%20ORDER%20BY%20component%20ASC%2C%20created%20DESC)
+
+If there are maintenance releases, they will be 78.2, 78.3, etc. (During ICU 78 development, the library version number was 78.0.x.)
+
+Note: There may be additional commits on the [maint/maint-78](https://github.com/unicode-org/icu/tree/maint/maint-78) branch that are not included in the prepackaged download files.
+
+## Common Changes
+
+* [CLDR 48](https://cldr.unicode.org/downloads/cldr-48)
+  ([alpha blog](https://blog.unicode.org/2025/09/unicode-cldr-48-alpha-available-for.html)):
+  * TODO: old news here
+  * No major data collection for existing locales; focus on bug fixes and structural improvements
+  * New regional variants: English in several European countries, and Cantonese in Macau (`yue_Hant_MO`)
+  * Improved RBNF (number spellout) and transliteration data
+* TODO: old news here
+* Subtle segmentation changes to make ICU fully conform to Unicode 16
+  * Word break: Root tailoring of colon reverted, Swedish & Finnish tailorings removed
+    ([ICU-22941](https://unicode-org.atlassian.net/browse/ICU-22941))
+    * These tailorings were introduced in ICU 72, but feedback has been negative,
+      and the UTC declined to adopt these changes.
+  * Line break: Fixed a bug in the line breaking of obscure sequences
+    ⟨no-break space, combining mark, hyphen, alphabetic character⟩
+    ([ICU-22986](https://unicode-org.atlassian.net/browse/ICU-22986)).
+  * Updated Indic grapheme clusters to use the latest `Indic_Conjunct_Break` data
+    ([ICU-22956](https://unicode-org.atlassian.net/browse/ICU-22956))
+* Time zone data (tzdata) version 2025b (2025-mar).
+
+## ICU4C Specific Changes
+
+* [API changes since ICU4C 77 (Markdown)](https://github.com/unicode-org/icu/blob/maint/maint-78/icu4c/APIChangeReport.md) / [(HTML)](https://htmlpreview.github.io/?https://github.com/unicode-org/icu/blob/maint/maint-78/icu4c/APIChangeReport.html)
+  * TODO: old news here
+  * New APIs for colloquial C++ use of C USet ([ICU-22876](https://unicode-org.atlassian.net/browse/ICU-22876))
+    and C UCollator ([ICU-22879](https://unicode-org.atlassian.net/browse/ICU-22879))
+    * These were added in ICU 76, but some of the new APIs did not actually compile with `U_SHOW_CPLUSPLUS_API=0`.
+      They have been fixed in ICU 77 and thoroughly tested.
+      USetElementIterator now returns std::u16string instead of icu::UnicodeString,
+      and therefore it and related APIs have been changed to `@draft ICU 77`.
+      ([ICU-22954](https://unicode-org.atlassian.net/browse/ICU-22954))
+    * For details about these APIs and an example see the
+      “C++ Header-Only APIs” section of the [ICU 76 Migration Issues](76.md#migration-issues).
+
+## ICU4J Specific Changes
+
+* [API Changes since ICU4J 77](https://htmlpreview.github.io/?https://github.com/unicode-org/icu/blob/maint/maint-78/icu4j/APIChangeReport.html)
+* TODO: old news here
+* The Java technology preview implementation of the CLDR MessageFormat 2.0 specification has been updated to incorporate the
+  [CLDR 46.1 spec](https://www.unicode.org/reports/tr35/tr35-74/tr35-messageFormat.html)
+  plus most but not all of the CLDR 47 changes.
+
+## Known Issues
+
+* TODO: old news here
+* The new MeasureUnit for `portion-per-1e9` works for formatting,
+  but when the new member function `getConstantDenominator()` is called on this unit,
+  it incorrectly returns 0. ([ICU-23045](https://unicode-org.atlassian.net/browse/ICU-23045))
+
+## Migration Issues
+
+* (none yet)
+
+### Migration Issues Related to CLDR
+* See [CLDR 48 migration issues](https://cldr.unicode.org/downloads/cldr-48#migration)
+
+## ICU4C Platform Support
+
+ICU4C requires C++17 and has been tested with up to C++23.
+
+We routinely test on recent versions of Linux, macOS, and Windows.
+
+We accept patches for other platforms.
+
+Windows: The minimum supported version is Windows 7. (See [How To Build And Install On Windows](../userguide/icu4c/build.html#how-to-build-and-install-on-windows) for more details.)
+
+## ICU4J Platform Support
+
+ICU4J works on Java 11..21 (at least).
+
+ICU4J should work on Android API level 21 and later but may require “[library desugaring](https://developer.android.com/studio/write/java8-support#library-desugaring)”.
+
+## Download
+
+### GitHub
+TODO rc tag:
+Source and binary downloads are available on the git/GitHub tag page: <https://github.com/unicode-org/icu/releases/tag/release-78-1>
+
+See the [Source Code Setup](../devsetup/source/) page for how to download the ICU file tree directly from GitHub.
+
+ICU locale data was generated from CLDR data equivalent to:
+
+* <https://github.com/unicode-org/cldr/releases/tag/release-48-beta1>
+* <https://github.com/unicode-org/cldr-staging/releases/tag/release-48-beta1>
+
+### Maven
+* TODO: not published yet
+* https://mvnrepository.com/artifact/com.ibm.icu/icu4j/78.1
+* https://mvnrepository.com/artifact/com.ibm.icu/icu4j-charset/78.1
+* https://mvnrepository.com/artifact/com.ibm.icu/icu4j-localespi/78.1