Recently I apparently corrupted my /boot/efi partition, I got according error messages at boot and a manual console to remount it.
I tried to reformat it (mkfs.vfat 32), reinstalled grub (grub-install), and updated fstab to the new UUID, however now it still fails to mount with FAT-fs (sda1): IO charset iso8859-1 not found.
UPDATE: since /boot/efi became corrupted I slapped together a vulgar script to recreate /boot/efi. Use at your own risk!
After finding the message above (by entering the manual recovery commandline offered and running dmesg | tail) I tried manual mounting. This failed as well.
Googling turned up that one should check whether the module nls_iso8859-1.ko could be loaded. So I tried running sudo modprobe nls_iso8859-1. This turned up an error about nort beeing able to open the dependency database. Recreating the dependency database with depmod fixed the issue.
depmodfixed it for me, Thanks! – Chiptus Jan 14 '19 at 07:40