The official Pokémon movie website has updated. Translations follow:
Trailer Coming on New Year's Day!!
The trailer will be shown in 2 days!!
The trailer is planned to air on New Year's Day 2019 between 0:00am and 0:30am in a commercial break during the "CDTV Special! New Year's Eve Premium Concert 2018->2019" on the TBS network*.
It is also planned to air on New Year's Day 2019 between 2:00am and 2:30am in a commercial break during the "Futtonda King Playoffs 2019" on the Nippon TV Network*.
It is also planned to air on New Year's Day 2019 between 18:30 and 19:00 in a commercial break during the "Hiroshi Sekiguchi's Tokyo Friend Park New Year's Day Special" on TBS*.
*Please note that the listed air times are approximate.
Source:
http://www.pokemon-movie.jp/