Text blocks should only accept a limitted range of characters

[rhubarbdog]

Describe the bug
Text blocks accept the following keyboard characters £ and ¬
i can also enter the degree symbol ° by entering the unicode 4 digit hexadecimal
both of these cases seem to be handled quite well using an 8bit ascii encoding
when i've pasted this hangul character 갎 and this symbol ☂ neither seem to be
handled well
To Reproduce
The hangul character and symbol were copied and pasted from this website
https://www.ltg.ed.ac.uk/~richard/unicode-sample.html
£ and ¬ can both be typed from my uk keyboard
° was entered as per this wiki

Expected behavior
because the only way to debug a blocks program on microbit is to use the basic.showString block which displays all characters ascii 31or less and ascii 128 or above as space so £10 appears as 10

Screenshots

or these blocks show the accepting blocks. I've coloured the text blocks yellow in the screen shot to make them stand out.

Desktop (please complete the following information):

• OS: Linux mint 18.2
• Browser mozilla firefox
• Version 63.0.3

[microbit-mark]

Related to microsoft/pxt#659
and
lancaster-university/microbit-dal#239

Unless it's possible to support additional ascii characters, is there a way we can notify users that the characters in the range 0-31 an 128+ cannot be displayed?

[abchatra]

Closing more than an year old bugs.

[microbit-mark]

Re-opening, as this is still a poor experience for people. As MakeCode supports more languages that make use of characters out of the supported range like Cyrillic , we can expect people to try to type in their own language. We should either prevent this as discussed in the original issue, or notify them somehow that the characters are not supported.

I have published https://support.microbit.org/support/solutions/articles/19000111896 which explains the issue, but it would be preferable to error in MakeCode.