dj i18n lang switcher template tag

lang_switcher.py

register = Library()


@register.simple_tag(takes_context=True)
def change_lang(context, lang=None, *args, **kwargs):
    try:
        request = context.get('request')
        path = request.path
        url_parts = resolve(path)

        if url_parts.url_name == 'model_i18n_slug_url':
            # e.g. /catalog/<slug>/, where `slug` is a django-parler translatable-field
            entry_obj = Entry.objects.distinct().get(
                translations__slug=url_parts.kwargs["slug"]
            )
            entry_obj.set_current_language(lang)
            url_parts.kwargs.update({'slug': entry_obj.slug})

        url = path
        cur_language = get_language()
        try:
            activate(lang)
            url = reverse(url_parts.view_name, kwargs=url_parts.kwargs)
        finally:
            activate(cur_language)

        qs = request.GET.urlencode()
        if len(qs) > 0:
            url_s += "?{}".format(qs)
        return url_s
    except Exception:
        return ''

      
# in templates
{% for lang_code, lang_name in LANGUAGES %}
    <link rel="alternate" hreflang="{{ lang_code }}" href="{% change_lang lang_code %}"> <!-- mind this is relative! -->
{% endfor %}