Assalaam o alaykum,
yup akhi u can do that, as stated in the hadith above.
tho du'as should preferably be done in the following order:
1) to try and find a dua in the sunnah
2) if u cant do tha aboev, then say the dua in arabic,
3) if u cant do that then in any language
example, if u want ur son to pass his medical exam, then u first look if there is any type of dua that the prophet (saw) done which u can use (on this subject).... if there isnt (which there isnt), then u simply just say the dua in arabic... if u dsont know arabic, then u say it in english (or whatever language).....
"However, I think it must be in arabic, or if it's in other language it should only be said in silence (at heart). "
should be said in silence? Dont know about that...