All of this list of missing translation keys in .po comes from the question editor views. I check every submenu on the right for each question type and found that those were missing:

1. Move out without warning
2. Default coordinates of the map when the page first loads. Format: latitude [space] longtitude
3. Sub-question validation equation
4. Enter a boolean equation to validate each sub-question.
5. Sub-question validation tip
6. This is a tip shown to the participant describing the sub-question validation equation.
7. Show Platform information
8. Show also the platform information of the participant
9. Manage label sets
10. Quick-add labels
11. The participant cannot upload a single file larger than this size
12. Position for 'Other:' option
13. Before no answer
14. After specific answer option
15. Resize
16. Crop
17. Crop or Resize
18. Horizontal scrolling
19. Show an horizontal scroll for the images instead of a vertical list. Needs JavaScript enabled.
20. Keep aspect-ratio
21. Keep images aspect ratio. Can be achieved by not setting both width and height. Needs JavaScript enabled.
22. Fix width of the images to this value. Leave empty to not change them.
23. Fixed height
24. Fixed width
25. Display theme options
26. Button size
27. Change button size
28. Small
29. Extra small
30. Maximum number of buttons in a row
31. Choose maximum number of buttons in a row
32. Allow searching of dropdown
33. Enable search function
34. on (searchable)
35. off (Searchable)
36. Display tick on selected items
37. Show a tick on the selected item in the dropdown
38. show tick
39. no tick
40. Width of dropdown should be the currently selected entry
41. Can be as wide as the entry that is selected, or fixed at the longest entry (default)
42. Width of dropdown to be currently selected entry
43. Width of dropdown to be longest entry
44. If the participant marks all options, uncheck all and check the option set in the "Exclusive option" setting
45. Indicates where the 'Other' option should be placed
46. The title of the subquestion after which the 'Other:' option will be placed if the position is set to 'After specific subquestion'
47. Label wrapper width
48. Slider start as this value. You can use Expression manager, but this must be a number before showing the page.
49. Use javascript function to remove text and uncheck checkbox (or use ExpressionScript Engine only).
50. Subquestion title for 'After specific subquestion'
51. Auto-add new line
52. Automatically add a new line when something is inserted
53. Add row icon
54. The icon used on the "add row"-button
55. Plus in circle
56. chevron down
57. arrwo down (there is a typo in this one. Should be Arrow down. Both keys don’t exists)
58. extra small
59. Replace choice header (default: "Your choices")
60. Replace rank header (default: "Your ranking")
61. Y-Scale
62. X-Scale
63. Without reorder
64. Allow only moving the answers
65. Viuzialisation (there is a typo in this one. )
66. Change visualization of the ranking question
67. Bubbles
68. Blocks
69. Buttons
70. Show number
71. Show the actual list numbers
72. Show handle
73. Show a handle for drag and drop

I also found the key in .po, but the following texts were not translated in view:

1. If the participant marks all options, uncheck all and check the option set in the "Exclusive option" setting
2. Force each answer option to have the same height (missing “.” At the end?)
3. Force the choice list and the rank list to have the same height (missing “.” At the end?)

The following keys are missing (can be seen on the 5 big buttons of home page):

1. List of available surveys
2. List of functions that are available with expression manager
3. Exit survey app

In the overview of a survey there is a button "export" which display the word "key" besides it. "key" should also be translated, and the key is missing in the .po.

I used the .po file from https://translate.limesurvey.org/projects/limesurvey-4/fr/default/ which was generated the 2022-08-22 in the morning.

I attached picture as example.