The short version: the English "unless" can be translated directly with an "or" construct and "da'i", such as "da broda gi'a da'i brode", if both cases can happen at the same time. If not, you need an "xor" construct instead ("gi'onai" in this case).
The long version: In analyzing "unless", it is helpful to have an example. For the "both can happen at the same time" case, we'll use "I have blue hair, unless my eyes are bad". The translation is "le kerfa be mi cu blanu .i ja bo da'i le kanla be mi cu spofu".
Call the former "BH" for blue hair, and the latter "EB" for "eyes are bad".
Truth table:
| BH | EB | BH or EB | Explanation |
| T | T | T | You have blue hair. It is also the case that your eyes are bad, however. |
| T | F | T | You have blue hair, and your eyes are just fine |
| F | T | T | Your eyes are bad, and your hair is not, in fact, blue. |
| F | F | F | The only false case: if you do not have blue hair, but your eyes are just fine, the original statement is false. |
For the "both cannot happen at the same time" case, we'll use "I'll kill you, unless you kill me first". Note that because of the word "first", both halves cannot be true at once. The translation is "mi ba catra do .i jo nai bo da'i do catra mi ca lo nu pu'o go'i".
Call the former "KY" for kill you, and the latter "KMF" for "kill me first".
Truth table:
| KY | KMF | KY or KMF | Explanation |
| T | T | F | False case: I killed you, and you killed me first. Patently impossible. |
| T | F | T | I killed you. |
| F | T | T | You killed me first. |
| F | F | F | False case: Nobody killed anybody, which violates the whole point of making the statement in the first place. |