Added jp lang

[tonymushah]

When loading special-eureka seasonal title this morning,
I got this error message

unknown variant `jp`, expected one of `ar`, `az`, `sq`, `bn`, `bg`, `my`, `ca`, `zh-ro`, `zh`, `zh-hk`, `hr`, `cs`, `da`, `nl`, `en`, `eo`, `et`, `tl`, `fi`, `fr`, `ka`, `de`, `el`, `he`, `hi`, `hu`, `id`, `it`, `ja`, `ja-ro`, `kk`, `ko`, `ko-ro`, `la`, `lt`, `mg`, `ms`, `mn`, `ne`, `kr`, `no`, `fa`, `pl`, `pt-br`, `pt`, `rm`, `ro`, `ru`, `sr`, `sk`, `es`, `es-la`, `sv`, `ta`, `te`, `th`, `tr`, `uk`, `vi`, `NULL`

I found the problem,
and this title Sasaki and Peeps: That Time I Got Dragged into a Psychic Battle in Modern Times While Trying to Enjoy a Relaxing Life in Another World Looks Like Magical Girls Are On Deck have a jp language variant on the attributes.title.
The jp variant is not registered in the ISO 639-1 standard.
Maybe some mistyping from the contributors ?
I don't know...

I just added jp language variant just in case.