I guess the Live system does not include localization files for Bulgarian
(only the installer is localized) and the relevant files must be downloaded
through "Language support" (or something similar) in the "System settings"
window of the newly installed system.
You need not reinstall but that may be the quicker way if you have not spent
much time configuring, installing new programs, etc. You could also discover
GRUB's password (the user is named "grub") from a live system: just read the
file /etc/grub.d/01_PASSWORD on the root partition of the installed system.
With this piece of information, you can then reboot (without the live system
plugged) enter GRUB's configuration, edit the boot line to pass the "single"
keyword among Linux's options, directly get a root terminal from which you
can execute 'passwd user', where "user" is the login of the user you want the
password modified. One more reboot and you can log in the system with that
user (and his new password).
To manually partition your drive, choose the last option (maybe called
"Something else") when the graphical installer asks you if Trisquel should
take the whole disk, etc. You can then erase existing partitions, create new
ones (with the types of filesystem of your choice) and decide what directory
(/, /home, etc.) will be on it. You obviously need a root partition (i.e.,
mounted at /) to proceed. Nothing is mounted on a swap partition. 4 GB of
swap probably is enough. The swap is not only used when the RAM is fulled but
also when hibernating the system. In that latter case, the whole content of
the RAM is dumped to the disk (I guess it is zipped first though) and that is
why users who want to hibernate any non-swapping system want as much swap as
they have RAM.
As for the chosen types of filesystems, Trisquel defaults to ext4 for the
system (a very well tested type of filesystem) and XFS for /home. XFS is said
to be particularly efficient to manage large files such as the user files (1
MB is large). It has a significant drawback though: it cannot be shrunk. But
since you plan to use 50 GB for the system, you should be safe: the system
will not need to take space over /home. If you feel a little adventurous, you
could try Btrfs, a modern and efficient type of filesystem with many
features. It is still said "experimental" in the kernel but many users have
been using it for years now.
