Converting/removing special characters / adding a text string at the beginning of the filename if not present

Hello, thanks for stopping by to read my questions. I have an ambitious/complex renaming project that I cannot figure out by myself, being new to regular expressions. Multiple operations need to be performed on a set of files.
First, I want to:


+++ Add a phrase to files with a specific filetype +++

I have a bunch of files with two different file extensions.
Files with filetypeB should always get or have a specific phrase at the beginning, filetypeA should not.

The names of the files are something like this:

food_ milk & éclairs 3.filetypeA

SpecificPHRASE_stringofwords[Hello] & über! V2.filetypeB


FiletypeB should start with a specific phrase (always the same one with lower and uppercase letters) followed by an underscore at the beginning, example:

SpecificPHRASE_

If a filetypeB file does not have the phrase, I want the renamer to add it. But if it is there, the addition should be skipped. It should never be applied to filetypeA files.

EDIT:
I have figured out a way to check if the phrase exists and to add it, also removing double entries such as SpecificPHRASE_SpecificPHRASE, and worked out that I can give the batch a filemask filter so only that filetype will be affected using the Replace Method with regular expressions.

Text to replace: (SpecificPHRASE_)*
Text to replace with: SpecificPHRASE_
Regular Expression option checked.

So I guess that part is solved, unless there is a better way to do this.


+++ Remove/convert special characters +++

The second thing I want to do is remove/convert special characters in all filenames.

The files may contain special characters such as @, ! &, ê, ä, ß, symbols, or letters from other alphabets such as Cyrillic.

1. Any Symbols like © or ♥ should be either removed entirely or converted to underscores.

2. I want the filenames to only consist of:

Letters (Aa-Zz),
numerals 0 to 9,
_ underscores and - dashes.

3. Any punctuation, brackets, and empty spaces should be converted to underscores, but existing dashes should remain untouched.

4. Special letters should be converted into plain letters, for example, é becomes e.

5. Characters like @ should become "At", & should become "And", ° should be "Degrees".

I already figured out how to solve the problem for 3 and 5. using the list replace method. This feature makes conversions of these characters into plain text very easy.

I also worked out a replacement containing [^\w\d_-] using regular expressions and it keeps only regular letters, numbers, _ and -, but also removes the special letters completely instead of replacing them with plain ones.

But if I go and put every special character and symbol into a list manually especially from other alphabets, it'll take forever. Is there a way to convert the special characters into a plain English alphabet? so, a Cyrillic Ф would become f, an ê would become e, and so on.

Any help is very much appreciated. I plan on creating a batch file to automate this, so if this takes multiple steps/cannot be put into one single operation, that would be okay.

Edit2: (I am trying to work on/solve the issue as best as I can):

I found a javascript script that can normalize accent characters here:
https://ricardometring.com/javascript-replace-sp ecial-characters

but I have no idea how to add the code to work in advanced renamer (a simple copy/paste into the script method field did not work and I have no idea how to code in js). Maybe someone here knows how to get it to work?