You would need around €622.10 (24,019.75 THB) in Thailand to maintain the same standard of life that you can have with €1,219.80 in Germany (assuming you rent a place to live in both cities). This assumes net earnings (after income tax).
If you eat out 4x a week in an inexpensive, and 1x a week in a mid-range restaurant you will pay €48.54 less in Thailand (€13.46) than in Germany (€62.00).
For monthly supply of groceries worth €203.30 in Germany you will pay €8.13 more in Thailand (€211.43). If you are an average smoker (1 pack per day), you'll spend €102.69 less on cigarettes each month than in Germany.
To buy an 85m2 apartment in Thailand city centre you will need €202,478.61 which is €126,954.19 less than in Germany (€329,432.80), however to buy one outside of the city centre you will need €114,580.89 which is €108,595.11 less than in Germany (€223,176.00).