Doing incomplete translations with sphinx is showing default language only?

After following the official workflow for translating files I find myself in a situation where the translation doesn't seem to work.

make gettext
sphinx-intl update -p /source/_build/gettext -l fr
set SPHINXOPTS=-D language=fr
make html

I have successfully created *.pot and *.po files and testwise translated parts of this *.po-file (other msgid's still default to "". Then I set the language to french and run make html again - but the text that I translated isn't displayed in french.

Nothing in the build output shows any hint on what's wrong:

C:\dev\ritune\docs>make html
Sphinx v4.1.2 in Verwendung
Lade Übersetzungen [fr]…erledigt
making output directory... erledigt
[autosummary] generating autosummary for: .roles.rst, configuration\add_modules\add_modules.rst, configuration\db_dump\db_dump.rst, configuration\index.rst, configuration\modules\config_dashboard\config_dashboard.rst, configuration\modules\index.rst, configuration\plotly_diagrams\plotly_diagrams.rst, data_explorer\data_explorer.rst, functions\asset_management\asset_management.rst, functions\dashboard\dashboard.rst, ..., system\index.rst, system\logs\logs.rst, system\main_menu\main_menu.rst, system\physical\physical.rst, system\proc\proc.rst, system\settings\settings.rst, system\tags\tags.rst, system\user_profile\user_profile.rst, system\users_roles\users_roles.rst, system\versions\versions.rst
loading intersphinx inventory from https://docs.python.org/3/objects.inv...
loading intersphinx inventory from https://www.sphinx-doc.org/en/master/objects.inv...
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 81 source files that are out of date
updating environment: [new config] 81 added, 0 changed, 0 removed
reading sources... [100%] system/versions/versions                             or2ntrol
looking for now-outdated files... none found
pickling environment... erledigt
checking consistency... preparing documents... erledigt
writing output... [100%] system/versions/versions                              r2ntrol
generating indices... genindex erledigt
writing additional pages... search erledigt
copying images... [100%] system/versions/version_numbering.svg                 1fcb54c2ee.png
copying downloadable files... [ 57%] modules/reporting_masks/Betriebsstatistik_Vorlage_20210514.xlsx_Betriebsstatistik_Vorlage_20210514.xlscopying downloadable files... [100%] system/alarms/ANSI-ISA-18.2 - Management of Alarm Systems for the Process Industries.PDF
copying static files... erledigt
copying extra files... erledigt
dumping search index in French (code: fr)... erledigt
dumping object inventory... erledigt
build abgeschlossen, 13 warnings.

Note that I excluded warnings that have to do with silly syntax mistakes I made in one of the files (the one I'm currently working on).

Is this expected behaviour or am I doing something wrong? I wanted to test the translation functionality and my *.po files.

Solution

I found the solution. Sphinx didn't actually pick up on the .mo (binary) files.

Steps to retrace for correct working:

Make sure you're in root directory and you see build and source directories
Using sphinx gettext will create *.pot files in build/gettext
Take those *.pot files and translate to *.po files using sphinx-intl update -p build/gettext -l fr (example for french/'fr'). This will create *.po files in a new folder locales which by default sits amongst the build and source dirs under root.
Translate *.po files
Now make sure that locale_dirs = ['../locales'] in conf.py points to the directory of the locales! This was not set up properly by default in my case. I had to change dir to parent ( ../ ) and use "locales" instead of the default "locale" to describe the path.
Run sphinx-intl build to create binaries (*.mo) out of *.mo files.
Set language to french for current terminal: set SPHINXOPTS=-D language=fr
make html