Localization support

Localization support. Finnish language added as a second language for the system. Also fixed an issue that could have shown direct error messages to the end users.

Needs testing before merge

tests/test_i18n.py

@@ -19,6 +19,7 @@ from babel.messages.extract import extract_from_dir
 
 from tjts5901.i18n import SupportedLocales
 from tjts5901 import __file__ as pkg_file
+from conftests import client, app
 
 @pytest.fixture
 def babel(app: Flask):