Sales are as reported on the Oricon website. There are 3 different lists that are compiled into this Top 10.
10) 5,900 Copies Sold Bokutachi wa Benkyou ga Dekinai
ぼくたちは勉強ができない 非日常の例題集
We Never Learn
No license for the light novel.
The Manga is licensed for English release by Viz.
An anime is currently airing.
9) 6,242 Copies Sold Shōsetsu eiga doraemon Nobita no getsumen tansa-ki
aka 小説 映画ドラえもん のび太の月面探査記
aka Doraemon the Movie 2019: Nobita’s Chronicle of the Moon Exploration
8) 6,247 Copies Sold Shinrei Tantei Yakumo Volume 11
心霊探偵八雲 11 魂の代償
Psychic Detective Yakumo
No English License for the light novel series
7) 6,283 Copies Sold Sentouin, Hakenshimasu! Volume 3
戦闘員、派遣します! 3
Combatants Will Be Dispatched!
http://www.lightnovels.site/2019/06/04/combatants-will-be-dispatched/
Licensed for English release by Yen On. Volume 1 will release August 20, 2019
6) 7,263 Copies Sold Isekai Cheat Magician Volume 9
異世界チート魔術師 9
Fantasy World Cheat Magician
No English License for the light novel series.
An anime is in production
5) 11,322 Copies Sold Re:Zero Kara Hajimeru Isekai Seikatsu Volume 19
Re:ゼロから始める異世界生活 19
Re:Zero Starting Life in Another World
http://www.lightnovels.site/2019/06/04/rezero-starting-life-in-another-world/
Licensed for English release by Yen On
4) 12,966 Copies Sold Isekai Nonbiri Nouka Volume 5
異世界のんびり農家 05
Farming Life in Another World
http://www.lightnovels.site/2019/05/31/farming-life-in-another-world/
No English License for the light novels
3) 13,527 Copies Sold Isekai Shokudou Volume 5
異世界食堂 5
Restaurant to Another World
http://www.lightnovels.site/2019/05/30/restaurant-to-another-world/
Licensed for English release by Seven Seas
2) 16,957 Copies Sold Bungo Stray Dogs BEAST
文豪ストレイドッグス BEAST
1) 23,625 Copies Sold Tensei Shitara Slime Datta Ken Volume 14
転生したらスライムだった件 14
That Time I Got Reincarnated As A Slime
http://www.lightnovels.site/2019/05/30/that-time-i-got-reincarnated-as-a-slime/
Licensed for English release by Yen On