RFR: 8264425: Update building.md on non-English locales on Windows [v3]

[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.

Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:

  * Add requirement on system locale as well.
  * Reorganize text to be more logical
  * Emphasize that the US locale should be used

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16694/files
  - new: https://git.openjdk.org/jdk/pull/16694/files/038407b3..6c1cd3b5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16694&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16694&range=01-02

  Stats: 62 lines in 2 files changed: 37 ins; 18 del; 7 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