missing entries in po files

we are translating po files to new languages and found that many entries are missing in po file

for example:

Compose tips like: "Lines and paragraphs are automatically recognized. The
line break,

paragraph and

close paragraph tags are inserted automatically. If paragraphs are not recognized simply add a couple blank lines."
"Forums"
"Recent subscribers"
"my subscription"
"invite friend"
some other entries in group like month name in calendar, "description of", "manager:", "age:", "% subscribers", "create %.." languages: "English" "Estonian" "Latvian" "Lithuanian" "Russian"
"Image Galleries"
image assist popup - most of entries.

how to translate these entries? and how i can find all po files non-excistant entries?