You mean "La Espada".

Yes you can, by using English Localization. Check out some of my mods; I use this extensively. I recommend using "Wolfgang Monk Amplified" as a point of reference, as it has the most rephrashing.

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If you want to do it from scratch, here's how:

1] Start with a localization folder that isn't English. I recommend picking a language with which you are familiar (I used French, so I guess I should have said "L'Epee").
"Data>Languages>French"

2] Copy it into your mod, so that you have
"Mod>Languages>French"
Rename the folder from French to English.

3] In any language folder except English and Example, you will find localization.xml, a localization folder, and a few other folders. The first two are important for what you intend.
You can edit localization.xml without disabling achievements. You can and should delete any item line that you do not intend to change the text for. If you do not, your mod will either change that text into the reference language you picked, or it will immediately crash when the file in question is missing. Also, be sure to change any image scaling from say 0.8 to 1.0, so that your text isn't shrunk to make room for accents.

4] Within the Localization folder, you will find .png files of every bit of text that appears in the game. The file names will be in english, but the images themselves will be in whatever language you have selected (so French for me). Carefully compare the files you need against the files you don't by looking at the lines in localization.xml and ensuring the filenames listed therein are contained in your folder. Delete the rest to reduce mod filesize.

5] Now the hard part. Use your pixel editor to change the text in the image to what you wish the text to say when your mod is running. This is hard because the packaged font images in the Necrodancer Data folder do not match the fonts that are used in the game. I had to jump around to different files to see what each letter looked like before putting it in the new image. This is doubly frustrating because there are two different types of font used by the game, "Small" and "Big".

6] Important note: The images need to remain the same pixel height (unless you're REALLY comfortable changing those particulars in the XML file), but you can make them any pixel width you please (minimum 8 pixels). So you can widen the image if you need room for more letters, or shrink it if you have a shorter description.

7] Devastatingly Important note: If you change character names, make sure you change them in the "Selected" folder too. If you delete that folder, you game will crash on scoreboards and in the level editor.

8] Be sure to test all the modes once you've made changes, to make sure you haven't accidentally excluded a file that is necessary. If you have, when that file would appear the game instead crashes to desktop.
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Making localization compatible across multiple mods is tricky, because the person installing the mod has to make changes to localization.xml in order for everything to work. As such, I recommend reserving it for your Bonewerks mod.