Add i18n support to KWin KCM: translate all strings, add translation infrastructure

[Copilot]

The KCM app had no i18n support — strings were a mix of bare QStringLiteral, Qt's tr(), and KDE's i18n(), with no translation catalog, no tooling, and no translator workflow.

C++ source fixes

• Set KDE i18n domain — KLocalizedString::setApplicationDomain("breezy_desktop_kwin") added at the top of the constructor, before setupUi(), so UI strings rendered by ki18n_wrap_ui use the correct catalog
• Convert all tr() → i18n() — 38 call sites: QObject::tr(), BreezyDesktopEffectConfig::tr(), and bare tr() in lambdas; .arg() chains rewritten as i18n("…%1", arg)
• Wrap missing strings — "%1 %2 connected", "No device connected", and the version label were bare QStringLiteral with no i18n at all

shortcuts.h — shortcut action labels

Changed actionText from QString to const char*, wrapped values with I18N_NOOP() for extraction, and call site uses i18n(shortcut.actionText):

// shortcuts.h
const char *actionText = I18N_NOOP("Toggle XR Effect");

// breezydesktopeffectkcm.cpp
action->setText(i18n(shortcut.actionText));

UI files — notr="true" for dynamic placeholders

Strings that C++ immediately overwrites at runtime don't belong in the catalog. Added notr="true" to:

• Version label in breezydesktopeffectkcm.ui (overridden in constructor)
• comboAddVirtualDisplay items 1080p, 1440p, Add custom… (combo is cleared and repopulated by populateResolutionCombo)
• Numeric labels 1920/1080 in customresolutiondialog.ui (set by slider valueChanged)
• ID/WxH placeholders in virtualdisplayrow.ui (overwritten by setInfo())

Translation infrastructure

Mirrors the structure used by the Python/GTK UI:

File	Purpose
kwin/po/LINGUAS	Same 12 languages as the Python UI
kwin/po/breezy_desktop_kwin.pot	POT template, ~80 strings with translator comments
kwin/po/<lang>/breezy_desktop_kwin.po	Stub PO files, all msgid populated, msgstr pre-filled where translations already exist in the Python/GTK UI
kwin/bin/update_pot_files	Dev script: extractrc → xgettext → msgmerge → msgfmt
kwin/TRANSLATING.md	Workflow docs for translators and maintainers

The dev script uses extractrc (from kdesdk-scripts) to convert Qt Designer .ui files into extractable C++ before running xgettext with full KDE keyword flags. Compiled .mo files are excluded from git (kwin/po/*/LC_MESSAGES/ in .gitignore) — ki18n_install(po) in CMake handles compilation at build time.

TRANSLATING.md covers: how to translate a .po file, how to add a new language, what to do after adding strings, and the do/don't for string marking in C++ and .ui files.

Pre-filled translations from the Python/GTK UI

20 strings are identical between the KCM and the Python/GTK UI. Existing translations for those strings have been copied into each language's KCM PO file so translators don't need to re-translate them:

1 day, 1 hour, All displays follow mode, Curved display, Default, Disabled, Enable multi-tap detection, Flat, Follow mode, Height, Horizontal, No device connected, Rearrange displays, Remove custom resolution, Remove virtual displays on disable, Request a token, Verify token, Vertical, Width, less than an hour

Coverage varies by language depending on what was already translated in the Python/GTK PO files (de, es, fr, it, ja, zh_CN got all 20; pt_BR got all 20; ru, sv, uk_UA got 10; pl got 0).

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[wheaney]

For any strings that are identical to their python/GTK counterparts, please copy over the existing translations.

[Copilot]

For any strings that are identical to their python/GTK counterparts, please copy over the existing translations.

Done in e84dee7. Found 20 strings shared between the KCM and Python/GTK PO files and copied all existing translations. Results by language:

• de, es, fr, it, ja, zh_CN — all 20 strings copied
• pt_BR — all 20 strings copied (note: the Python PO file has "All displays follow mode" and "Remove virtual displays on disable" mapped to the "Curved display" translation — that's a pre-existing issue in the Python translations)
• ru, sv, uk_UA — 10 strings copied; the other 10 had empty/fuzzy entries in the Python PO so were left blank
• pl — 0 strings available in the Python PO; all entries remain empty

The matched strings are: 1 day, 1 hour, All displays follow mode, Curved display, Default, Disabled, Enable multi-tap detection, Flat, Follow mode, Height, Horizontal, No device connected, Rearrange displays, Remove custom resolution, Remove virtual displays on disable, Request a token, Verify token, Vertical, Width, less than an hour.