Sorry, but it's hard for me to help if I cannot reproduce the problem on my own device.

If you disable bluetooth in the Settings app, does the problem still occur when you select all text?

Can you maybe make a short video that shows the problem and upload it to Dropbox or a similar service so I can see exactly what is happening? 

Hello, please have a look at the Settings app -> General -> Language & Region.

You can set a preferred order of languages there using the Edit button in the top right corner. Maybe you have German set before English for some reason?

JSON does not support multi-line strings. You need to escape new line characters with \n and tab characters with \t.

You can use a JSON validator like https://jsonlint.com to check whether it is a valid JSON file.

This works:

{
  "uuid": "E3435C11-14CF-4DE6-A0D8-EE5ADC2F0D5C",
  "category": "Markdown",
  "templates": [
    {
      "name": "Frontmatter",
      "fileExtension": "md",
      "snippet": "---\ntitle: ${1:untitled}\ndate: DATE\nlayout: post.hbs\ncollections: posts\ndraft: true\ndesc: $2\n---\n"
    }
  ]
}

I've also added tab stops, so that you can enter a title after creating a file with this template and hit tab to jump to the description field.

Thanks for letting me know about this problem. This used to work on iOS, too, but Apple changed the behavior when the backspace key is pressed. This will be fixed in the next update.

This should work since Textastic 6.4.

Yes, you are right, the syntax definitions need an update.

No, sorry, I'm not aware of such an issue. Do you have any more information on when this happens? Which version of the app and iOS, which device?

You cannot make it appear with a single tap on the editor?

Hello, what happens when you try to preview the HTML file in Safari (button in the top right corner -> Preview in Safari)?

Hello,

you are right - at the moment, many files cannot be opened because the file extension is not known to the system. I plan to allow the user to open any file using the "Open…" command in a future update.