可以考虑以下的写法:
“ToWhomItMayConcern
ThisistocertifythatXXXisundergoinganinternshipprogrammeinourCompanysince01July2011,hispositionisAssistanttoHRManager.Hismaindutiesarearrangingforroutinemeetings,recruitment,orientationfornewstaffmembers,andsoon.Duringthisperiod,Mr.XXXwasobservedtobehard-working,attentiveandpositiveatwork.Throughtoutthepastyear,hehadgradullysecuredagoodunderstandingoftheoperationoftheCompanyandalsopossessedthenecessaryskillsandexperiencerequiredforthejob.
(最好加上:ShouldtherebeanyfurtherenquiryregardingtheinternshipofMrXXX,pleasefeelfreetowriteto/emailtheundersigned.)
DatedthisXXJune,2012
(Signature&Companychop)”
以上这样会比较明确,符合商业、企业一贯做法.
希望帮到你.