Gunnar played an important role in Debian-packaging and distributing IBus Avro, a phonetic keyboard for the Bangla (my native) language, as well such packages for as many other languages.
I can easily set up the tools for writing Bangla in my computer partly due to the efforts of Gunnar.
Despite not being a native speaker of this language, he would put extreme efforts to help with the bug reports in GitHub, many of which were reported in Bangla. He would patiently use online translators to understand the cause of frustration of the users.
He once commented about the decline in the number of questions in Ask Ubuntu about IBus Avro, which means, people are having less trouble configuring it. In other words, his efforts for distributing the software were very successful.
He also had a thorough knowledge of how to configure input methods in all kinds of desktop interfaces as well as in all versions of Ubuntu, which had different underlying settings.
He was an active contributor to IBus and other similar tools, and helped with the development and packaging of writing tools in many languages, not just Bangla.
While I did not know him personally, I interacted with him on several occasions in Ask Ubuntu and GitHub. He was always very kind in answering my questions in Ask Ubuntu.
While Gunnar's absence will be felt, his contributions will continue to benefit millions of users who write in their native scripts on Debian based operating systems. He will definitely be remembered.