Translated using Weblate (Ukrainian)

Currently translated at 66.8% (1711 of 2562)
Merge remote-tracking branch 'origin/QA_3_5' into QA_3_5
Translated using Weblate (Galician)

Currently translated at 99.9% (2560 of 2562)
Translated using Weblate (Galician)

Currently translated at 100.0% (2562 of 2562)
Translated using Weblate (Ukrainian)

Currently translated at 73.6% (1885 of 2562)
Translated using Weblate (Ukrainian)

Currently translated at 74.5% (1909 of 2562)
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Currently translated at 41.8% (1072 of 2562)
Translated using Weblate (Galician)

Currently translated at 100.0% (2562 of 2562)
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Currently translated at 80.5% (2063 of 2562)
Translated using Weblate (Korean)

Currently translated at 42.2% (1081 of 2562)
Translated using Weblate (Ukrainian)

Currently translated at 81.0% (2076 of 2562)
Translated using Weblate (Russian)

Currently translated at 99.9% (2560 of 2562)
Translated using Weblate (Russian)

Currently translated at 100.0% (2562 of 2562)
Translated using Weblate (Korean)

Currently translated at 42.3% (1084 of 2562)
Revert "remove unused variables"

This reverts commit cb9e34d42a36c98835454f9181eabf593889654e.

-> $error_header, $lang and $dir are used in the included file
libraries/error.inc.php
add comment why variables are still needed
Merge pull request #145 from zixtor/master

When unable to display chart, show appropriate error message.
Coding style improvements
fix bug #3783, instanciate class before calling static method
Throw error if no sql query is set