Jaehn will be the first Lithuanian citizen to serve in Germany's army.
He applied for the Lithuanian government's sanction six weeks ago.
As proposed by Interior Minister Tomas Žilinskas, the issue was included in the agenda of the government's meeting on Wednesday, as, according to information available to the minister, Jaehn intends to leave for Germany on Saturday.
He will be the first Lithuanian citizen during the 26 years of independence to serve in Armed Forces of a foreign country, according to the Interior Ministry.
In 2010 and 2014, Lithuania's government allowed two citizens to serve in the Danish army, in addition to another Lithuanian serving in the US Armed Forces since 2008.