Wrongly rendered option labels in form fields under some circumstances
From Joomla! Documentation
There is a known issue in form fields of type radio and list (presumably also others that extend the list field class) concerning option label translating.
Error reported[edit]
Option value label rendered incorrectly. Duplicate option labels.
Versions affected[edit]
Reported for Joomla 3.9.14 but older and newer versions are also affected for sure.
What is the cause[edit]
Example[edit]
The field definition:
<field name="moderator" type="radio" label="COM_EXAMPLE_SPEAKER_TYPE">
<option value="0">COM_EXAMPLE_SPEAKER</option>
<option value="1">COM_EXAMPLE_SPEAKER_MODERATOR</option>
</field>1) The name of the field is moderator.
2) Look at the language strings of the option labels:
COM_EXAMPLE_SPEAKER
COM_EXAMPLE_SPEAKER_MODERATOR
3) At least the second one is present in a language ini file of the extension or otherwise loaded.
Resulting issue: The first one will lead to an error (= wrong option label) because Joomla magic is transforming it to COM_EXAMPLE_SPEAKER_MODERATOR while collecting the options for the output.
In other words: Joomla combines the language string COM_EXAMPLE_SPEAKER and the field name moderator to a wrong label COM_EXAMPLE_SPEAKER_MODERATOR because COM_EXAMPLE_SPEAKER_MODERATOR exists in the language ini file.
How to fix[edit]
Use another field name than moderator.
OR
Use another language string than COM_EXAMPLE_SPEAKER_MODERATOR for option label.
OR
Use another language string than COM_EXAMPLE_SPEAKER for option label.