Warning: Unable to use English input method

[skyper]

What steps will reproduce the problem?

Do not really know.
I am using an external keyboard with German layout and default 105+ nodeadkeys German setting.
JOSM language setting is unchanged (system defaults) and locale is LANG=en_US.utf8 with LANGUAGE= unset.

What is the expected result?

No repeating warning and info messages in the console.

What happens instead?

Console is spawned with messages:

2021-07-01 17:00:01.311 INFO: Using English input method
2021-07-01 17:00:01.311 WARNING: Unable to use English input method
2021-07-01 17:00:01.311 INFO: Restoring input method to _US
2021-07-01 17:00:09.805 INFO: Using English input method
2021-07-01 17:00:09.806 WARNING: Unable to use English input method
2021-07-01 17:00:09.806 INFO: Restoring input method to _US
2021-07-01 17:00:41.667 INFO: Using English input method
2021-07-01 17:00:41.668 WARNING: Unable to use English input method
2021-07-01 17:00:41.668 INFO: Restoring input method to _US
2021-07-01 17:00:52.892 INFO: Using English input method
2021-07-01 17:00:52.892 WARNING: Unable to use English input method
2021-07-01 17:00:52.893 INFO: Restoring input method to _US
2021-07-01 17:01:28.839 INFO: Using English input method
2021-07-01 17:01:28.839 WARNING: Unable to use English input method
2021-07-01 17:01:28.839 INFO: Restoring input method to _US

Please provide any additional information below. Attach a screenshot if possible.

Can not really tell when it started but not that long ago. Might have some more time after the weekend to try different revisions and different keyboards.

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2021-06-28 23:03:35 +0200 (Mon, 28 Jun 2021)
Revision:17943
Build-Date:2021-06-29 01:31:02
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (17943 en) Linux Debian GNU/Linux 10 (buster)
Java version: 11.0.11+9-post-Debian-1deb10u1, Debian, OpenJDK 64-Bit Server VM
Look and Feel: com.formdev.flatlaf.FlatDarkLaf
Environment variable LANG: en_US.utf8
System property file.encoding: UTF-8
System property sun.jnu.encoding: UTF-8
Locale info: en_US
Desktop environment: GNOME

Last errors/warnings:
- 08589.866 W: Unable to use English input method
- 08601.090 W: Unable to use English input method
- 08637.037 W: Unable to use English input method
- 08685.429 W: Unable to use English input method
- 08699.632 W: Unable to use English input method
- 08721.870 W: Unable to use English input method
- 08829.967 W: Unable to use English input method
- 09191.703 W: Unable to use English input method
- 09211.047 W: Unable to use English input method
- 09290.976 W: Unable to use English input method