documentation/extensions/odoo_theme/layout_templates/language_switcher.html

<div class="o_languages">
	<div class="dropdown">
        {%- if alternate_languages|length > 0 %}
            <button class="btn btn-sm dropdown-toggle"
                    id="languages"
                    data-bs-toggle="dropdown">
                {{ language }} {# The current language #}
            </button>
        {%- else %}
            <button class="btn btn-sm dropdown-toggle"
                    id="languages"
                    disabled="">
                {{ language }} {# The current language #}
            </button>
        {%- endif %}
        <ul class="dropdown-menu" aria-labelledby="languages">
            {%- for alternate_language, language_code, url in alternate_languages %}
                <li><a class="dropdown-item" href="{{ url }}">{{ alternate_language }}</a></li>
            {%- endfor %}
        </ul>
	</div>
</div>