Hakka is a diverse language, with many dialects
Hakka phrasebook uses the Moiyan dialect. The Moiyan dialect is considered the standard dialect by most authorities, including the Chinese government. This dialect is mainly spoken within Guandong and Taiwan.
Although Moiyan is considered to be one dialect, there is still considerable variation between the way it is spoken in different areas. The version of Hakka used in this app is specifically what is spoken in the New Territories of Hong Kong.