{%- if language == "ja" %}
[日本語] <a href="{{ pathto('../en/', 1) }}{{ pathto(pagename, 0, '.') }}">English</a>
{%- elif language == "en" %}
<a href="{{ pathto('../ja/', 1) }}{{ pathto(pagename, 0, '.') }}">日本語</a> [English]
{% else %}
unknown language: {{ language }}
{%- endif %}