There are tons of errors offered in the link which are breaking german law and eu law.
For the marriage certificate take a look at Visa handbook C(2010) 1620 final section III family members of eu citizen, subsection 3.7 burden of proof last sentence:
"A Member State may require that the relevant documents are translated, notarised or legalised where the original document is drawn up in a language that is not understood by the authorities of the Member State concerned or if there are doubts as to the authenticity of the document."
https://ec.europa.eu/home-affairs/sites ... ted_en.pdf
If the marriage certificate is legalised from the thai embassy it is legalised.