The problem isn't that you can't scale, the issue is that you can't scale with the current business model.
Looking at your website (Applingua), I have noticed a few things which can be done to solve this.
First of all, your pricing strategy is wrong and part of the reason is what, you yourself admit that you don't charge enough as a small project is costing you money and a large project costs you time.
To fix your pricing strategy, I would implement the following changes:
First of all, I would implement a set fee for a certain amount of words and then $0.xx per word afterwards. This would instantly prevent "small projects" costing you money as for example you can decide upto 500 words = $xx then $0.xx per word after so words under this amount would be "profitable" for you so to speak since you're getting paid for more words than you are actually translating.
Additionally, I would also offer an "express" service like PSD to HTML services offer with premiums being charged on delivery times. Many small teams/single devs use these and pay for the "premium" feature of express service - you definitely should implement this into your service.
For example, turnaround time would be offered to all customers for instance at 5 working days, and then they can pay an additional fee for the express service i.e. $10+ for 3 days, $20+ for 48 hours , $35+ for 24 hours and even $50+ for the same day (providing it is before a certain time) - Obviously, these are example express pricing fees and turnaround times so you can edit these to suit your needs.
Upon, doing all of this I would also slightly increase your prices slightly by a couple of pennies on each of your offerings.
This would mean that you would have a new pricing structure, that would give you an inital set fee for your work and even more money for certain jobs than you would initally receive as well as, additional revenue from your express service. Likewise, the slight increase will also help your profitability and help solve the fact that you don't charge enough.
With regards to being able to take on more work via employing someone then, there are a few methods and options available to you for this.
First of all, you could employ a student on a part-time basis (since you can't guarantee a full time position) meaning you could take in more work as well as, provide them with relevant work experience especially if they are a language student.
Secondly, you should focus on automating as much of your service as you can - even more than you are already doing. This may mean having to refer to vWorker or Automated tools etc for various aspects and using your language/freelancers language skills to "tidy" up the work so to speak whilst, maintaining the quality.
Moreover, you could also employ a Virtual Assistant as well to automate/scale-up some of aspects of your work. You can hire some VA's for $250/month and they'll work pretty much full-time for you - and you can "train" them to do various tasks for you - whether thats focusing on the marketing etc to take some burden off your shoulders and automate/scale up other aspects of your business.