app-doc/gimp-help: Add IUSE="nls" and fix LINGUAS logic

[ulm]

Follow standard gettext behavior:

• USE="-nls": build only English documentation (and ignore LINGUAS)
• USE="nls" and unset LINGUAS: build all available languages
• USE="nls" and empty LINGUAS: build only English
• USE="nls" and nonempty LINGUAS: build listed languages if supported

See also the following mailing list posting for an explanation: https://archives.gentoo.org/gentoo-dev/message/38914ce4a7a228d2d29fb623346fba10#L29

Bug: https://bugs.gentoo.org/891709

[ulm]

CC @band-a-prend

[gentoo-bot]

Pull Request assignment

Submitter: @ulm
Areas affected: ebuilds
Packages affected: app-doc/gimp-help

app-doc/gimp-help: @band-a-prend, @gentoo/proxy-maint

Linked bugs

Bugs linked: 891709

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Docs: Code of Conduct ● Copyright policy (expl.) ● Devmanual ● GitHub PRs ● Proxy-maint guide

[gentoo-repo-qa-bot]

Pull request CI report

Report generated at: 2023-05-07 06:28 UTC
Newest commit scanned: 8cee870
Status: ✅ good

There are existing issues already. Please look into the report to make sure none of them affect the packages in question:
https://qa-reports.gentoo.org/output/gentoo-ci/13e181053d/output.html

[gentoo-repo-qa-bot]

Pull request CI report

Report generated at: 2023-05-07 07:18 UTC
Newest commit scanned: 67014ec
Status: ✅ good

There are existing issues already. Please look into the report to make sure none of them affect the packages in question:
https://qa-reports.gentoo.org/output/gentoo-ci/546d2d1849/output.html

[gentoo-repo-qa-bot]

Pull request CI report

Report generated at: 2023-05-07 09:33 UTC
Newest commit scanned: 557b73d
Status: ✅ good

There are existing issues already. Please look into the report to make sure none of them affect the packages in question:
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[gentoo-repo-qa-bot]

Pull request CI report

Report generated at: 2023-05-07 10:03 UTC
Newest commit scanned: 664deb1
Status: ✅ good

There are existing issues already. Please look into the report to make sure none of them affect the packages in question:
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