Katha or gatha, is similar to paritta in Theraveda Buddhism.
It is a prayer, to respect the holy entity of the amulet, and to request for blessing.
Katha is usually written in Pali, Thai, Khmer, or Sanskrit language.
Unlike mantra or dharani in Vajrayana Buddhism and Hindhuism, which does not encourage translation, katha can be translated freely, for the devotees to understand the real meaning of it.
However, some have suggested that even after translation, it is still best to chant the katha in its original language.
Katha has its root from three believes: buddhism, hindhuism and occultism.
Understanding which katha belongs to which origin is not easy, as it requires some knowledge of its language and background.
Simply knowing who consecrate the amulet mostly will not help, unless you know the master very well, as some Buddhist monks consecrate using Hindhuism or Occultism knowledge or katha.