-lah’ is a particle that is always attached to the preceding word. It is to mark the predicate when the predicate is out of its normal position. It is never obligatory.
The particle -lah is quite often attached as a suffix to commands and prohibitions. It doesn’t have an easily describable meaning. Basically it adds polite emphasis. But it seems to have a variety of effects depending on context. For example, while it can make a command or prohibition more imperious and emphatic, in other contexts it can also ameliorate a command, making it sound pleading, or more polite, or less brusque.
Lah is especially commonly attached to intransitive verbs when they are used in commands.
- Tertipulah kamu. You were tricked.
- Percayalah padaku. Just trust me.
- Hasilnya tidaklah terlalu baik. The result is not too good.
- Hubungan kami sangatlah dekat. Our relationship is very close.
- Tinggalah dia seorang diri. He is the only one left.