Well I'm sorry but thats not true. MKEK has license to produce both MP5, MP5K and MP5SD models for decades (the first MP5A2 were produced by MKEK since 1967 onwards if I recall correctly). You can check It out from their website and also from their weapons exhibition stands too. Also like you said MKEK models have Turkish "E-T-S" (Emniyet: safety, Tek: single, Seri: serial) markings also seen from on my sample photo. But according to the weapons I have luck to inspect and the source I have asked the issue, they have been transioned the original S-E-F markings specially for the export models for years ago. And also for the Ukraine case the original sale news has announced on Turkish media around a month ago . So in my humble opinion we can safely say the MP5s were sourced from Turkey to..
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www.mkek.gov.tr
And here are some of my photos taken from a MKEK weapons exhibition in 2015. You can spot the various trigger groups on MP5 models, including semi-auto "0-1" model and both Turkish "E-T-S" and original "S-E-F" models displayed together.
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That could be the original reason but in the past some of the other European countries have also bought MKEK made German guns. Such as Georgia, Azerbaijan and Poland with MP5, FYROM with G3 and Norway with MG3 due to their low cost compared to German producers.