SharePoint online lookup column translation issue

Question

I have a SharePoint online site collection.. and created a list named "TestList" with two columns "testcol1" & "testcol2" ( columns are site column and created manually from UI). I have localized these two columns for es-ES and named as "testcol1 ES" and "testcol2 ES" using the translation import functionality... and localization is working fine..

Now, I am creating a third site column which will be of type lookup and named as "lookupcol". It is referencing the "TestList" and have lookup with "testcol1"...

Once the browser locale is changed to es-ES, I can see the columns are translated in site collection level.. but when I am opening the lookup column "lookupcol" - it's associated column "testcol1" is showing in the default language.. which should have translated automatically...

Can someone tell me if anything is wrong on the followed step... If you require anymore info to help me understand and resolve this issue, please let me know...