Ok, I've figured out a general approach, that I've tested the concept on, but I haven't completely implemented it. Because it's sort of ugly and it requires more work than I'm willing to put into it right now. Here's the idea:
For each field that you want to use in your filename, you develop an MC expression based on replace() for each accented character that you want to translate. For example, you probably want to translate é to e. There are a LOT of these to translate if you want to catch absolutely everything. Here's an example I did based on some songs in my library. This is NOT an exhaustive list. It's just a test I was working with.
replace(replace(replace(replace([Name],à, a),á, a), é, e), ó, o)
This works on the name field, but could be applied to Artist or Album or whatever. Next step:
Build a new Library field for each field you want to use in your file name. This is necessary because you don't want to overwrite the data in your Name, Album, or Artist fields. You just want a container to hold the new strings that don't have accents. For my tests, I called these:
Name_ascii
Artist_ascii
Album_ascii
To add these fields, go to: Tools > Options > Library & Folders > Manage Library Fields > Add New Field
Now, to populate these fields:
1. Highlight a group of files you want to work on. This could be just a few files, or hundreds or thousands. Please test on a few first!
2. Press Alt-<enter> to bring up the tagging pane on the left.
3. Find the field you want to build. Let's say you are working on Name, so we are going to find the Name_ascii field. Click in that field to edit it.
4. Paste in the replace expression with an = sign in front like this: =replace(replace(replace(replace([Name],à, a),á, a), é, e), ó, o)
Repeat the above with Artist and Album if you want, pasting into the Artist_ascii and Album_ascii fields. Make sure your replace() expression references the correct field: [Artist] to populate Artist_ascii and [Album] to populate Album_ascii.
Now all of your new non-accented fields are populated. So now you can use Rename, Move, and Copy to rename the files based on these new fields. For example, you might make the directory rule:
[Artist_ascii]/[Album_ascii]
The file rule might be something like:
[Track #]_[Name_ascii]
The real work here is building up the replace() expressions. My example above only replaces 4 sets of characters. If your song collection only references 4, 5, 6 characters with accents, this might not be too bad. If it uses a dozen or more, it's going to require a lot of careful evaluation and testing. The nice thing is, once you've built the replace() expression for one category (like Name for example), you can reuse it for the others. Just change the field name inside.
I hope this makes sense. Let me know if I can help further.
Good luck.
Brian.