Slack Notification: UTF-8 Support

Weird text characters come if you use national UTF-8 characters.

In Task Title is OK!
But a problem in Description and Discussion.

For example
Instead of signs:
aćęłńóśźż ĄĆĘŁŃÓŚŹŻ

Slack comes with:
& Auml; & # 133; & Auml; & # 135; & Auml; & # 153; & Aring; & # 130; & Aring; & # 132; & oacute; & Aring; & # 155; & Aring; & ordm; & Aring; & frac14; & Auml; & # 132; & Auml; & # 134; & Auml; & # 152; & Aring; & # 129; & Aring; & # 131; & Oacute; & Aring; & # 154; & Aring; & sup1; & Aring; & raquo;