With the following ABAP code, various special characters can be removed from a string using a regular expression. This example shows removing all Unicode characters from the lv_string variable.

"remove all unicode characters from lv_string

replace all occurrences of regex '[[:unicode:]]' in lv_string with ''. 

Here are more regular expressions for specific character groups:

[[:alnum:]]	Alphanumeric characters
[[:alpha:]]	Letters
[[:blank:]]	Spaces and horizontal tabs
[[:cntrl:]]	Control character
[[:digit:]]	Digits
[[:graph:]]	Graphic special characters
[[:lower:]]	Lowercase
[[:print:]]	Displayable characters
[[:punct:]]	Punctuation marks
[[:space:]]	Spaces, tabs and feeds
[[:unicode:]]	Unicode character (code greater than 255)
[[:upper:]]	Capital letters
[[:word:]]	Alphanumeric characters and _ (underscore)
[[:xdigit:]]	Hexadecimal digits

Source: help.sap.com - Regex