Egbert,
I received the files of this database in trial mode and was able to analyse them more calmly.
I converted the database to text to try with Sublime Text and VSCode to locate the correct encoding, but what I could see is that it is practically irreversible.
To fix it the best chance is to convert the database to text and use “Replace” to batch correct the errors:
./i2id database > new_database.txt
This link explains a possible cause: https://php-de.github.io/jumpto/utf-8/
This site (https://dencode.com/) tries to find the correct encoding for text, I tried to play some database snippets and no satisfactory result.
My hypothesis is that this database was converted to UTF8 and used as ISO8859-1, because according to what I read in a forum the error happens when the file is with one encoding but is displayed as another, causing a mix up.
If there is a purer version of this database could help, but right now I only see the replacement as a resolution.
There are even tables for this, but it is a lot of work:
É -> É â€œ -> " †-> " Ç -> Ç Ãƒ -> à é, 'é à -> À ú -> ú • -> - Ø -> Ø Ãµ -> õ à -> í â -> â ã -> ã ê -> ê á -> á é -> é ó -> ó â€" -> - ç -> ç ª -> ª º -> º à -> à