Add translation strings for True Retention table (#3745)

* Add translation strings for True Retention table

* Hard-code strings to make pylint happy

ftl/core/statistics.ftl

@@ -103,14 +103,28 @@ statistics-counts-separate-suspended-buried-cards = Separate suspended/buried ca
 ## comparison to the "desired retention" parameter of FSRS, which forecasts
 ## future retention. True Retention is the percentage of all reviewed cards
 ## that were marked as "Hard," "Good," or "Easy" within a specific time period.
+##
+## Most of these strings are used as column / row headings in a table.
+## (Excluding -title and -subtitle)
+## It is important to keep these translations short so that they do not make
+## the table too large to display on a single stats card.
+##
+## N.B. Stats cards may be very small on mobile devices and when the Stats
+##      window is certain sizes.
 
 statistics-true-retention-title = True Retention
 statistics-true-retention-subtitle = Pass rate of cards with an interval ≥ 1 day.
 statistics-true-retention-range = Range
 statistics-true-retention-pass = Pass
 statistics-true-retention-fail = Fail
+# This will usually be the same as statistics-counts-total-cards
+statistics-true-retention-total = Total
 statistics-true-retention-count = Count
 statistics-true-retention-retention = Retention
+# This will usually be the same as statistics-counts-young-cards
+statistics-true-retention-young = Young
+# This will usually be the same as statistics-counts-mature-cards
+statistics-true-retention-mature = Mature
 statistics-true-retention-all = All
 statistics-true-retention-today = Today
 statistics-true-retention-yesterday = Yesterday

ts/routes/graphs/TrueRetention.svelte

@@ -41,12 +41,12 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
     <InputBox>
         <label>
             <input type="radio" bind:group={mode} value={DisplayMode.Young} />
-            {tr.statisticsCountsYoungCards()}
+            {tr.statisticsTrueRetentionYoung()}
         </label>
 
         <label>
             <input type="radio" bind:group={mode} value={DisplayMode.Mature} />
-            {tr.statisticsCountsMatureCards()}
+            {tr.statisticsTrueRetentionMature()}
         </label>
 
         <label>

ts/routes/graphs/TrueRetentionCombined.svelte

@@ -29,13 +29,13 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
         <tr>
             <td></td>
             <th scope="col" class="col-header young">
-                {tr.statisticsCountsYoungCards()}
+                {tr.statisticsTrueRetentionYoung()}
             </th>
             <th scope="col" class="col-header mature">
-                {tr.statisticsCountsMatureCards()}
+                {tr.statisticsTrueRetentionMature()}
             </th>
             <th scope="col" class="col-header total">
-                {tr.statisticsCountsTotalCards()}
+                {tr.statisticsTrueRetentionTotal()}
             </th>
             <th scope="col" class="col-header count">
                 {tr.statisticsTrueRetentionCount()}