Comment # 7 on bug 1167315 from Canwei Luo

Thank you very much.
I fixed my problem with your help.

Yes, recently, I had installed sogou_pinyin with the repo as follow: 
http://download.opensuse.org/repositories/M17N/openSUSE_Leap_15.1/M17N.repo.
And it seems conflicts with my Leap 15.0.
And I had installed fast_gettext manally:
gem install fast_gettext

So, my solution is as follow:
(1) remove the M17N repo(Leap 15.1)
sudo zypper rr 1  ## 1 is the index number of M17N after `sudo zypper lr`

(2) add the M17N repo(Leap 15.0)
sudo zypper ar -f
https://download.opensuse.org/repositories/home:/MargueriteSu:/branches:/M17N/openSUSE_Leap_15.0/home:MargueriteSu:branches:M17N.repo

(3) update repo
sudo zypper update

(4) uninstall sogou-pinyin/yast2(including kde_yast and
yast2_basis)/fast_gettext
sudo zypper remove sogou-pinyin
sudo zypper remove yast2-ruby-bindings
sudo zypper remove ruby2.5-rubygem-fast_gettext
sudo gem uninstall fast_gettext

(5) reinstall yast2
sudo zypper install patterns-kde-kde_yast
sudo zypper install patterns-yast-yast2_basis

(6) reinstall sogou-pinyin 
sudo zypper install sogou-pinyin

My yast2 rebirths.