Sublanguage

add_action('sublanguage_custom_switch', 'my_custom_switch', 10, 2);

/**
* @param array of WP_Post language custom post
* @param Sublanguage_site $this The Sublanguage instance.
*/
function my_custom_switch($languages, $sublanguage) {

?>
<ul>
<?php foreach ($languages as $language) { ?>
<li class="<?php echo $language->post_name; ?> <?php if ($sublanguage->current_language->ID == $language->ID) echo 'current'; ?>">
<a href="<?php echo $sublanguage->get_translation_link($language); ?>"><?php echo $language->post_title; ?></a>
</li>
<?php } ?>
</ul>
<?php

}

How to have language switch in navigation menus ?
If you are using menus and you want the language switch into a menu,
go to Display > Menu, open option drawer and verify 'language' is selected.
Then add as much 'language item' as you have languages.
You can even distribute languages on different hierarchy level.
If you need current language to be on the first level and further language on the second, you will also want to check current language first in Settings -> Sublanguage
Post title, content or excerpt does not translate as expected in my theme
First go to Sublanguage>Settings and verify the relevant post type is set to be translatable.

Then verify you are using the proper filters in you template file.

For echoing post title, you need to ensure ´the_title´ filter is called.

// echoing post title inside the loop
the_title();

// echoing post title outside the loop
echo get_the_title($some_post->ID);

// but...
echo $post->post_title; // -> Does not translate

For echoing post content, you need to ensure ´the_content´ filter is called.

// echoing content inside the loop
the_content();

// or...
echo apply_filters('the_content', get_the_content());

// but...
echo $post->post_content; // -> Does not translate
echo get_the_content(); // -> Does not translate

// echoing post content outside the loop:
echo apply_filters('sublanguage_translate_post_field', $some_post->post_content, $some_post, 'post_content');

Same for Excerpts.

Permalinks are automatically translated, inside or outside the loop:

// echoing permalink
echo get_permalink($post->ID);

Some texts in my theme do not translate as expected, like 'Comment', 'Leave a Reply', etc.
In your template files, verify texts are properly localized, and language packages are properly installed.
How can I access the current language for custom usage?
Use the global $sublanguage, like this:

global $sublanguage;
echo $sublanguage->current_language // -> WP_Post object
echo $sublanguage->current_language->post_title; // -> Français
echo $sublanguage->current_language->post_name; // -> fr
echo $sublanguage->current_language->post_content; // -> fr_FR

Alternatively you can use a sublanguage filter to call a user function with $current_language value in parameters:

Function to use in your template file:

echo apply_filters('sublanguage_custom_translate', 'text to translate', 'my_custom_translation', 'optional value');

Code to add in your function.php file:

/**
* @param string $original_text. Original text to translate.
* @param WP_Post object $current_language
* @param mixed $args. Optional arguments
*/
function my_custom_translation($original_text, $current_language, $optional_arg) {

if ($current_language->post_name == 'fr') {

return 'texte traduit en français!';

}

return $original_text;

}

Note: of course, for a basic usage like this, you should use the standard localization way: __('text to translate', 'my_domain').
How to translate wordpress options like 'blog name' or 'blog description' ?
Go to Sublanguage>Translate Options and try to find the corresponding option key. Options may be nested in a data tree.
How to translate texts in widgets?
Go to Sublanguage>Translate Options and find the corresponding widget option name (like 'widget_somthing'). Expand items with value corresponding to 'DATA' until you find the text you need to translate.
How to translate nav menu items?
Your nav menu items that are linked to translated posts, pages or terms should be automatically translated.

If you need to translate custom link or to change the default value for items name, you can select "Nav Menu Item" in "Translate post types" section of Sublanguage settings.
Then open Sublanguage>Nav Menu Item and edit like a normal post.
How to make a custom post-meta value translatable?
Go to Sublanguage settings and select custom post-meta key in the checkbox list under "Translate Meta". A meta key needs to be at least used once to appear in this list.
How to make post thumbnails translatable (different picture for each language)?
Go to Sublanguage settings and select '_thumbnail_id' in the checkbox list under "Translate Meta". At least one thumbnail must be set before metakey appears in this list.
How to access language data in javascript for ajax usage ?
Add this action to enqueue a small script to define values in javascript:

add_action('init', 'my_init');

function my_init() {

}

This will first define a global in javascript. Use console.log(sublanguage) to explore it.

Furthermore, a small script will automatically add a language attribute in every jquery ajax call. You can change this language using sublanguage.current (in javascript). This language will be used if you need to get/update posts/terms using ajax.
How to import/export my blog with translations ?
You cannot export or import using the wordpress builtin tool while Sublanguage is active. It just does not work yet. But this feature will come in a future release.

If you want to create a custom importer for posts and terms, you can use these 2 functions:

These functions are documented in sublanguage/include/admin.php. See examples on github.
Will this plugin affect my site performance?
Yes it will, unfortunately. A few more database queries are necessary to load every page.
If performance drops noticeably, you may want to install a cache plugin. Sublanguage have been sucessfully tested with WP Super Cache and W3 Total Cache (with default settings).

Sublanguage also works with SQLite Integration plugin.
My language is not in the language list
Use any language instead, then update, then edit language title, slug and locale, then update again.