Language URL for Statamic 2

Usage:

Intended to help build a language toggle for Statamic 2. For example, in a English and French site where English is the default language, you can use {{ lang_url locale="fr" }} and {{ lang_url locale="default" }} in your templates to easily switch languages of the current page:

{{ if locale == "en" }}
  <a href='{{ lang_url locale="fr" }}'>Français</a>
{{/if}

{{ if locale == "fr" }}
  <a href='{{ lang_url locale="default" }}'>English</a>
{{/if}