How to replace Unicode LaTeX strings in Python 3.13?

I am trying to replace multiple instances of a given Unicode string in a group of LaTeX files. For example, the original line reads:

\greek{῾Ρώμην}\nft{2}{ \greek{Ῥώμη, ῥώμη}: \textit{bodily strength, might, Roma, Rome}}

And I would replace it with the following line:

\greek{῾Ρώμην}\nft{2}{ \greek{Ῥώμη, ῥώμη}: \textit{Roma, Rome, bodily strength, might}}

I have created a substitute file (subs.tsv) to hold all my replacements for these files. It follows a pattern of target-substitution across two columns. For the above replacments, it would read thus:

"\greek{῾Ρώμην}\nft{2}{ \greek{Ῥώμη, ῥώμη}: \textit{bodily strength, might, Roma, Rome}}" "\greek{῾Ρώμην}\nft{2}{ \greek{Ῥώμη, ῥώμη}: \textit{Roma, Rome, bodily strength, might}}"

When I run this through Python, however, I get a mass of gobbledygook that looks like this:

Øgreekæ῾ΡώμηνåØnftæ2åæ ØgreekæῬώμη, ῥώμηå: Øtextitæbodily strength, might, Roma, Romeåå" "Øgreekæ῾ΡώμηνåØnftæ2åæ ØgreekæῬώμη, ῥώμηå: ØtextitæRoma, Rome, bodily strength, mightåå

Current coding effort runs like this:

#!/usr/bin/env python3

from os import listdir
from glob import glob

fileset = '.'

with open('subs.tsv', encoding='utf-8') as subsfile:
    subs = subsfile.readlines()



for filename in glob('./*tex'): 
    with open(filename, encoding='utf-8', errors='ignore') as f:
        filecontents = f.read()
        for subline in subs:
            subitem = subline.split('\t')
            target = subitem[0]
            sub = subitem[1]
            filesubbed = filecontents.replace(target, sub)

Thanks in advance for your consideration and any help you can offer.