Bug: Smart menu language restriction does not respect switching language with the language switcher

[abias]

This is a follow-up issue to #300 and is related to #376

Steps to reproduce:

• Login as admin
• Go to Site administration -> Language -> Language packs and install the german language pack
• Go to Site administration -> Language -> Language settings, set the language of the site to english and enable the langmenu
• Go to Site administration -> Appearance -> Boost Union -> Smart menus
• Create a new smart menu
• Set the location to main navigation
• Set an arbitrary menu title
• Set "Restrict visibility by language" to "German"
• Login as teacher
• Go to your user profile settings and set your preferred language to german
• Verify that you see the smart menu in the main navigation
• Go to your user profile settings again and set your preferred language to english
• Verify that you do not see the smart menu in the main navigation
• Go to the language menu in the user menu and switch the language to german

Expected result:

• You see the smart menu in the main navigation again

Actual result:

• You do not see the smart menu in the main navigation again

Analysis:

• The "Restrict visibility by language" seems not to really respect the language which is currently used on the current Moodle page.