docs(README): add instructions to translate the theme

Makefile

@@ -0,0 +1,25 @@
+MESSAGE_CATALOG_NAME = sphinx
+
+.PHONY: help
+help:
+	@echo "Please use \`make <target>' where <target> is one of"
+	@echo "  extract       to extract translatable strings into POT files"
+	@echo "  init          to initialise a PO file for a new language"
+	@echo "  update        to update existing PO files"
+	@echo "  compile       to compile updated PO files"
+
+.PHONY: extract
+extract:
+	pybabel extract -o iati_sphinx_theme/locale/$(MESSAGE_CATALOG_NAME).pot -F babel.cfg iati_sphinx_theme
+
+.PHONY: init
+init:
+	pybabel init -i iati_sphinx_theme/locale/$(MESSAGE_CATALOG_NAME).pot -d iati_sphinx_theme/locale --domain=$(MESSAGE_CATALOG_NAME) -l ${lang}
+
+.PHONY: update
+update:
+	pybabel update -i iati_sphinx_theme/locale/$(MESSAGE_CATALOG_NAME).pot -d iati_sphinx_theme/locale --domain=${MESSAGE_CATALOG_NAME}
+
+.PHONE: compile
+compile:
+	pybabel compile --directory=iati_sphinx_theme/locale --domain=${MESSAGE_CATALOG_NAME}

README.md

@@ -73,3 +73,37 @@ To run a local version of the theme with another project, e.g. `my-docs`, take t
    pip install sphinx-autobuild
    sphinx-autobuild docs docs/_build/html
    ```
+
+### Translation
+
+Follow the steps below to translate the theme's built-in strings from the HTML templates in the `iati_sphinx_theme` directory.
+The message catalog name is `sphinx.[pot|po|mo]` and is found in the `iati_sphinx_theme/locale` directory.
+These are bundled with the published theme in order for consumers to have access to the translations.
+
+A `Makefile` exists to make running the commands easier:
+
+1. Extract text into `.pot` files
+
+   ```
+   make extract
+   ```
+
+2. Update existing `.po` files based on `.pot` files
+
+   ```
+   make update
+   ```
+
+3. Optionally, initialise a `.po` file for a new language
+
+   ```
+   make init lang=es
+   ```
+
+4. Add translations to the `.po` files
+
+5. Compile to `.mo` files (only applies to the theme's built-in strings, so that they can be bundled with the theme)
+
+   ```
+   make compile
+   ```