Installation:
Download the ZIP file from here and unpack ist whereever you like. It will create a folder 'sunshine' that contains the program. It requires GTK3 and Python3.

Configuration:
Open the file 'sunshine.cfg' in an editor and customize the settings to your needs. Not all settings must be changed. The list below describes the settings that should be changed to meet your requirements:

(only change the parameters that are listed below; don't change the other parameters in the config file)

[api]
# Name of the city for the API
city = Zurich
# Name of the city as displayed on screen
city_translated = Zürich Wetter
# Language code for the API
language = de

[week]
# Day names as displayed on screen
1 = Montag
2 = Dienstag
3 = Mittwoch
4 = Donnerstag
5 = Freitag
6 = Samstag
7 = Sonntag

[gui]
# x position of the window's top/left corner
pos_x = 1300
# y position of the window's top/left corner
pos_y = 30
# x-width of the window
width = 340
# y-height of the window
height = 880
# background color of the window
bg_color = #E5E5E5
# transparency value of the window background: 0 = opaque, 100 = transparent
transparency = 100
# color of the text
text_color = #FFFFFF
# font name and font size of the text
font_name = ubuntu 24
# text shown beside the temperature value
temp_unit = Grad
# weather symbol horizontal offset: distance from left edge
img_x = 110
# weather symbol vertical offset: distance from day name
img_y = -30
# show 'city_translated' on screen: yes, no
show_city = yes

How to start and stop the application:
Make the file 'sunshine.sh' executable. Open a terminal and navigate to the 'sunshine' folder. Start it with './sunshine.sh'. If you don't like the appearance of the window, change it in the config file. If everything is fine, you could create a launcher for the application. Just copy an existing desktop file in folder '/usr/share/applications/' and change the settings and its name to 'sunshine.desktop'.

The application is stopped by simply clicking on it's window.

Here is an example on how the content of the desktop file could look like (you must change the pathes):

[Desktop Entry]
Name=Sunshine
Name[de]=Sunshine
Comment=Weather forecast
Comment[de]=Wettervorhersage
Exec=/home/ralf/dev/python/sunshine/sunshine.sh <-- change this path
Icon=/home/ralf/dev/python/sunshine/sunshine.svg <-- change this path
Terminal=false
Type=Application
Categories=Utility;
StartupNotify=false