Component language file is coppied but does not work

Question

I am just trying to create backend component and I can't get the language file to work.

This is my xml manifest (the important part):

<media destination="com_displaygroups" folder="media">
  <filename>index.html</filename>
  <folder>css</folder>
</media>

<administration>
  <!-- Administration Menu Section -->
  <menu link='index.php?option=com_displaygroups'>COM_DISPLAYGROUPS</menu>
  <submenu>
    <menu view="groups">COM_DISPLAYGROUPS_BY_GROUPS</menu>
    <menu view="users">COM_DISPLAYGROUPS_BY_USERS</menu>
  </submenu>
  <!-- Administration Main File Copy Section -->
  <!-- Note the folder attribute: This attribute describes the folder
  to copy FROM in the package to install therefore files copied
  in this section are copied from /admin/ in the package -->
  <files folder="admin">
    <!-- Admin Main File Copy Section -->
    <filename>index.html</filename>
    <filename>displaygroups.php</filename>
    <filename>controller.php</filename>
    <folder>models</folder>
    <folder>views</folder>
    <folder>language</folder>
  </files>
  <languages folder="admin/language">
    <language tag="en-GB">en-GB/en-GB.com_displaygroups.sys.ini</language>
  </languages>
</administration>

I just want one language file because that 3 strings in the manifest are all what I need. When I install the component i get the message:

Warning JInstaller: :Install: File does not exist C:\xampp\htdocs\just-joomla\tmp\install_56dd839e79478\admin\language\en-GB\en-GB.com_displaygroups.sys.ini

but I can see that Joomla adds language file inside administrator\components\com_displaygroups\language\en-GB\ the en_GB.com_displaygroups.sys.ini

Can anyone tell me what am I doing wrong here? :(

Edit1\ My file tree inside component:

com_displaygroups
│   displaygroups.xml
│   tree.txt
│   
├───admin
│   │   controller.php
│   │   displaygroups.php
│   │   index.html
│   │   
│   ├───language
│   │   │   index.html
│   │   │   
│   │   └───en-GB
│   │           en_GB.com_displaygroups.sys.ini
│   │           index.html
│   │           
│   ├───models
│   │       groups.php
│   │       index.html
│   │       users.php
│   │       
│   ├───sql
│   │   │   index.html
│   │   │   
│   │   └───updates
│   │       │   index.html
│   │       │   
│   │       └───mysql
│   │               0.0.1.sql
│   │               index.html
│   │               
│   └───views
│       │   index.html
│       │   
│       ├───groups
│       │   │   index.html
│       │   │   view.html.php
│       │   │   
│       │   └───tmpl
│       │           default.php
│       │           index.html
│       │           
│       └───users
│           │   index.html
│           │   view.html.php
│           │   
│           └───tmpl
│                   default.php
│                   index.html
│                   
└───media
    │   index.html
    │   
    └───css
            display-style.css
            index.html

Answer 1

You can also ship the language files within your component in the language folder as I do with DPFields https://github.com/Digital-Peak/DPFields/blob/master/com_dpfields/admin/dpfields.xml#L48. After installation the language files are still in your component folder. Joomla will auto detect the translation files.

Check out that the filename in the manifest file and the folder tree are the same. Otherwise they don't get loaded. If it still doesn't work, then it can be that you have an error in your language file. Set Debug Language to yes in your Joomla configuration, it will tell you which files could be loaded and which ones not.

Answer 2

Try this:

<languages folder="admin">
    <language tag="en-GB">language/en-GB/en-GB.com_displaygroups.sys.ini</language>
</languages>

and remove

<folder>language</folder>

From the section of your manifest.