RFR: 8264425: Update building.md on non-English locales on Windows

[Magnus Ihse Bursie]

Update the build documentation to reflect the fact that non-English locales are only supported on a "best effort" principle, and add instructions how to install the necessary language pack to Visual Studio.

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Commit messages:
 - 8264425: Update building.md on non-English locales on Windows

Changes: https://git.openjdk.org/jdk/pull/16694/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16694&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8264425
  Stats: 78 lines in 2 files changed: 78 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16694.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16694/head:pull/16694

PR: https://git.openjdk.org/jdk/pull/16694