Translate the interface, with German as the second language

CLAUDE.md

@@ -161,6 +161,8 @@ not finished until the README shows the application as it now is.
   screenshots match what ships. A pull request that adds one and leaves the
   README describing the previous application is incomplete, the same way one
   without a test is.
+- **A new user-visible string is not done until it is wrapped for Qt
+  translation and present in the German catalogue.**
 - **A minor release checks the README and the screenshots before the version
   bump.** A patch carries corrections and needs no pass. A minor carries
   something new — and the screenshots are the part that rots silently, because

README.md

@@ -27,6 +27,10 @@ composite. MatteLoop is the whole path from that clip to that loop:
 - **Open Preferences** from the gear button to choose or clear the output
   directory.
 
+The interface is available in English and German. Change the language in
+Preferences from the gear button; the choice applies after restarting
+MatteLoop.
+
 The result is lossless and genuinely transparent — an alpha channel, not a
 matte painted onto a colour.
 

docs/building.md

@@ -37,6 +37,21 @@ build also includes Nuitka 2.8.10, PyAV 16.1.0, Pillow 12.3.0, NumPy 2.5.2,
 `rembg` 2.0.75, and CPU `onnxruntime` 1.29.0. Do not install a second Python
 environment for the build; run the commands below from the repository root.
 
+## Translation catalogues
+
+Regenerate the English and German Qt translation sources after changing
+user-visible copy:
+
+```sh
+uv run --frozen --no-sync pyside6-lupdate -extensions py -no-obsolete src/matteloop -ts resources/matteloop_en.ts resources/matteloop_de.ts
+```
+
+Compile the checked-in sources into the catalogues loaded by the application:
+
+```sh
+uv run --frozen --no-sync pyside6-lrelease resources/matteloop_en.ts resources/matteloop_de.ts
+```
+
 ## Licensing gate
 
 The repository's original code, documentation, and visual assets use 0BSD.

packaging/pysidedeploy.spec

@@ -74,6 +74,8 @@ extra_args =
 	--include-module=PIL.WebPImagePlugin
 	--include-data-files=resources/model-manifest.json=resources/model-manifest.json
 	--include-data-files=resources/model-provenance.json=resources/model-provenance.json
+	--include-data-files=resources/matteloop_en.qm=resources/matteloop_en.qm
+	--include-data-files=resources/matteloop_de.qm=resources/matteloop_de.qm
 	--include-data-files=LICENSE=LICENSE
 	--include-data-files=THIRD_PARTY_NOTICES.md=THIRD_PARTY_NOTICES.md
 	--include-data-files=legal/GPL-3.0.txt=GPL-3.0.txt

pyproject.toml

@@ -51,6 +51,10 @@ packages = ["src/matteloop"]
 [tool.hatch.build.targets.wheel.force-include]
 "resources/model-manifest.json" = "matteloop/resources/model-manifest.json"
 "resources/model-provenance.json" = "matteloop/resources/model-provenance.json"
+"resources/matteloop_en.qm" = "matteloop/resources/matteloop_en.qm"
+"resources/matteloop_de.qm" = "matteloop/resources/matteloop_de.qm"
+"resources/matteloop_en.ts" = "matteloop/resources/matteloop_en.ts"
+"resources/matteloop_de.ts" = "matteloop/resources/matteloop_de.ts"
 "resources/fonts/IBMPlexSans-Regular.ttf" = "matteloop/resources/fonts/IBMPlexSans-Regular.ttf"
 "resources/fonts/IBMPlexSans-SemiBold.ttf" = "matteloop/resources/fonts/IBMPlexSans-SemiBold.ttf"
 "resources/fonts/IBMPlexMono-Regular.ttf" = "matteloop/resources/fonts/IBMPlexMono-Regular.ttf"