What does DIN 5008 exactly say about percent character?

Question

On Wikipedia: Percent sign, there is following claim:

In German, the space is prescribed by the regulatory body in the national standard DIN 5008.

I can't speak German, so I can't read the whole standard. What does it say about it? Should there be a space or not?

And is what the standard says the same what is actually taught in German grammar?

Answer 1

This is a question about typography in German texts.
Typically, typography is not a subject in grammar teaching.
That results in a lot of awful typography all around.

As witnessed at Prozentzeichen:

Wie bei Maßeinheiten wird zwischen die Zahl und das Prozentzeichen ein geschütztes Leerzeichen gesetzt. Der Duden empfiehlt hier, einen kleineren, festen Zwischenraum zu verwenden. Nach dem Chicago Manual of Style soll allerdings in englischsprachigen Texten kein Zwischenraum zwischen eine Zahl und ein Prozentzeichen gesetzt werden.

Meaning: contrary to English rules (CMS), where a number should be followed without a space, in German texts the number is followed with a nonbreaking space. (And Duden for example even recommends a narrower spatium [Schmales Leerzeichen, thin space]. That is extremely rare to find except in texts by people who really care about typography.) – Exact rules for English texts should follow the style guide that fits your application.

Non-breaking space means that between number and sign will never be a line break. Even that is quite rare in actual use, but very recommended. While most aspects of these special format spaces rules are nearly invisible to an untrained eye, a new line starting with a percent sign is.

A non-breaking space can be encoded in HTML with   and is accessed for most editors on different platforms as follows:

Windows:    Alt+0+1+6+0 (doesn't always work)
Mac:        ⌥Opt+Space
Linux(X11): Compose, Space, Space or AltGr+Space

A spatium encoded in HTL with   and is accessed

Windows:     Alt+2+0+0+6 (there are five versions between alt+2001 and alt+2007)
Mac:         Shift+Opt+Space
Linux:       Ctrl+Shift+Space

To illustrate:

• 100% version without space
• 100 % version with thin space
• 100 % version with normal non-breaking space for comparison

Answer 2

To complete the excellent answer by @LangLangC here the relevant passage from DIN 5008:2011-04 Schreib- und Gestaltungsregeln für die Textverarbeitung as requested in OP:

8.7 Prozent- und Promillezeichen

Vor dem Prozent- und Promillezeichen wird ein Leerzeichen gesetzt. Das Leerzeichen entfällt bei Ableitungen.
2 % Skonto
3 1/4 % Zinsen
38%ig

o/oo (mit Kleinbuchstaben o) oder ‰
2 o/oo
2 ‰ Maklergebühr

Which translates roughly to:

A space is to be placed in front of percent or permill signs. But not if used in derivative forms such as 38%ig

(The second paragraph is about how to use o/oo as an replacement for the permill sign ‰)