Here is a list of suggestions I have noted down. I list them in random order.

COMBINED BUTTONS FOR NEXT ITEM AND RELEVANT STATUS
First selecting status and then clicking a button takes unnecessary time.
It would be better if one could do these two things in one and the same click.
Thus, I propose the following submit buttons:
---Needs translation & Next
---Needs editing & Next
---Needs proofreading & Next
---Ready to commit & Next
You may want to put other button values/titles though (than the ones suggested above).

SIDE COLUMN WITH SHORTCUTS TO RECENT ENTRIES
(1) It would be nice to have a side column (perhaps on the right-hand side of the screen) with shortcuts to the last couple of items/entries most recently translated, or to the few couple of entries that immediately precede or follow the current one.
If one needs to go back etc.
(2) Alternatively or in addition, I suggest as a minimum that there should be a Back button if you want to go back to the immediately previous item, the one you just translated.

ABILITY TO COPY SOURCE TEXT INTO TARGET TEXT INPUT FIELD
Some way to automatically and immediately import the source text into the target text input field. (Similar to Wordfast's CTRL+S.)
Implementation: Perhaps the source text string could be stored in Javascript and there could then be a small icon image link; when the icon is clicked, Javascript would import the string into the target text input field.

ABILITY TO BROWSE/JUMP ITEMS ACCORDING TO A SPECIFIC STATUS
It should be possible to revise/browse items/entries only with a specific status. For instance to go through, one by one, items with status "Needs editing", or any items which still have not been finalized, etc.

MORE EFFICIENTLY ORGANIZED SPACE OVERALL
(1) All input fields (e.g. for status) and buttons should be as high up on the screen as possible, so that I won't have to scroll down the browser window to find them (thereby losing time and getting slightly frustrated each time...).
Remember that some users (like myself...) like to use large screen fonts - which means that we see less content at the top of the page and may need to scroll down to see more.
(2) In line with the above comment, I would recommend _minimizing_ the web site header on all translation interface pages. (Remove the site logo from such pages, or use a much smaller version of it... It just takes unnecessary space on these sorts of pages. The translation page doesn't need to look great or give a great corporate impression - it just needs to be practical and function efficiently as a workspace (which includes minimal download time, by the way).)

QUESTION/COMMENT/ISSUE INPUT FIELD
There should be a small input area next to each item/entry, where the translator can ask a question to the client or note an issue, e.g. if some term is ambiguous or clarification otherwise is necessary.

PROGRESS INDICATOR
It would be nice with indicators showing how far I have gotten through the total document. For instance: "You are currently at entry 58 out of 113 (XXX% done)."

CUSTOMIZED DISPLAY OF TARGET TEXT
It should be possible for the translator to set the font settings of at least the font used in the target text input field, such as font family, font size, etc.
At least font size...