Many abstracts in English are UNSTRUCTURED and are one paragraph in length and have no SUB-HEADINGS

And when structured, the sub-heading are usually like those suggested here

Background, Introduction, Objectives, Methods, Results, Conclusions

https://earthweb.ess.washington.edu/roe/Web_page_314/ESS314/...


examples here also
https://earthweb.ess.washington.edu/roe/Web_page_314/ESS314/...

SO I think OUTLINE could indeed work here, although the Abstract iself is an OUTLINE.
As each subheading seems to be an outline you might need to break it down into appropriate sub-headings like 1 Objective (Purpose) II Background/In General etc.

Or you could indeed retain the word PLAN (if that is usual in French abstracts??). But it would not really look like an English abstract in my view (and I have written several and have reviewed many more).

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Note added at 15 hrs (2020-06-06 14:47:38 GMT)
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OOPS I realised just now I [osted the same link twice. Sorry, meant to post this one

https://en.wikipedia.org/wiki/Abstract_(summary)

"Structure
An academic abstract typically outlines four elements relevant to the completed work:

The research focus (i.e. statement of the problem(s)/research issue(s) addressed);
The research methods used (experimental research, case studies, questionnaires, etc.);
The results/findings of the research; and
The main conclusions and recommendations
It may also contain brief references,[6] although some publications' standard style omits references from the abstract, reserving them for the article body (which, by definition, treats the same topics but in more depth).

Abstract length varies by discipline and publisher requirements. Typical length ranges from 100 to 500 words, but very rarely more than a page and occasionally just a few words.[7] An abstract may or may not have the section title of "abstract" explicitly listed as an antecedent to content. Abstracts are typically sectioned logically as an overview of what appears in the paper, with any of the following subheadings: Background, Introduction, Objectives, Methods, Results, Conclusions.[citation needed] Abstracts in which these subheadings are explicitly given are often called structured abstracts. Abstracts that comprise one paragraph (no explicit subheadings) are often called unstructured abstracts..."

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Note added at 4 days (2020-06-10 19:20:08 GMT) Post-grading
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Glad to have helped