Is it self-plagiarism to repurpose a government report into a journal article?
Can I use the same texts/paragraphs from the report to write journal articles? In other words, does it consider plagiarism to do that? I am the author of both, the report and the research papers. Does the final report for a project consider a published work?


The short answer to your questions are it depends. The long answer is likely yes, you can probably publish both with some caveats. 

In principle, there is nothing wrong with using a project report as the basis for a journal article. Speaking from experience, I have co-authored several completion reports that were used as the basis for manuscripts. For example, the Great Lakes Fisheries Commission Sea Lamprey Control Broad publishes completion reports on their webpage, but still encourages the investigators to publish the work in peer reviewed journal articles. However, there are some important considerations:


Make sure your funding agency is okay with you publishing their report. On a more positive note, some funding agencies will encourage you to publish. 
Is your completion report public and is it citable? You may or may not need to cite your previous work. Mentioning the completion report in your cover letter would also help address this problem with the journal.
The completion report likely will not be formatted correctly or written in a style suitable for a journal. Likely your methods section will be okay and possibly the results section. Most likely, the introduction and discussion will need to be adapted to fit the journal's style and tone.