I’m Polish. For some reason on my system left alt is different key than right alt:
$ xev | awk -F'[ )]+' '/^KeyPress/ { a[NR+2] } NR in a { printf "%-3s %s\n", $5, $8 }'
64 Alt_L # left alt
108 ISO_Level3_Shift #right alt
I type Polish characters with right alt It’s pretty convenient for me 
Also: Take a look at this discussion:
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