Before you can use a parameter as a selection criteria in a player segment you need to configure it as a Player Metric. This can be achieved by selecting the Metric options for the parameter in the Game Parameters Editor, reachable from the SETUP navigation menu in your game.
You can create metrics out of Numeric or Text based parameters,
STRING based metrics can be used to reveal the FIRST or LAST value of a particular parameter
PARAMETER based metrics can be used to track FIRST, LAST, MIN, MAX, COUNT, SUM of numeric parameters.
To configure the STRING based userLanguage parameter as a metric select the "First" and "Last" metric checkboxes as shown below.
Give the system a few minutes to pickup your changes then you will be able to create a Manual Segment that uses your userLanguage metric as a selection criteria.